feat(web/m7-recurring-scans): admin Scan schedule section

Adds a "Scan schedule" section to the admin overview page between
the existing Library Scan and Cover Art sections. Mode picker
(Off / Every N hours / Daily / Weekly) with conditional interval /
time / day inputs. Save button disabled until local state diverges
from the server state. "Next scan: in N hours (timestamp)"
inline indicator when mode != off.

formatRelative is a static helper (recomputes on render); operator
sees the configuration confirmation at a glance — not a countdown
timer.

admin.test.ts mock extended with createScanScheduleQuery returning
mode='off' default. New test asserts the section renders. Existing
assertions still pass.

web/src/routes/admin/+page.svelte

@@ -10,13 +10,17 @@
     createAdminQuarantineQuery,
     createScanStatusQuery,
     createCoverageQuery,
+    createScanScheduleQuery,
+    updateScanSchedule,
     approveRequest,
     rejectRequest,
     resolveQuarantine,
     deleteQuarantineFile,
     deleteQuarantineViaLidarr,
     refetchMissingCovers,
-    triggerScan
+    triggerScan,
+    type ScanSchedule,
+    type ScanScheduleMode
   } from '$lib/api/admin';
   import { qk } from '$lib/api/queries';
   import { copyForCode } from '$lib/api/error-copy';
@@ -224,6 +228,89 @@
     return new Date(iso).toLocaleString();
   }
 
+  // ---- Scan schedule ----
+  const scheduleStore = $derived(createScanScheduleQuery());
+  const scheduleQ = $derived($scheduleStore);
+  const schedule = $derived(scheduleQ.data);
+
+  let scheduleLocal = $state<{
+    mode: ScanScheduleMode;
+    interval_hours: number;
+    time_of_day: string;
+    weekly_day: number;
+  }>({
+    mode: 'off',
+    interval_hours: 6,
+    time_of_day: '03:00',
+    weekly_day: 7,
+  });
+  let scheduleSaving = $state(false);
+
+  $effect(() => {
+    if (schedule) {
+      scheduleLocal = {
+        mode: schedule.mode,
+        interval_hours: schedule.interval_hours ?? 6,
+        time_of_day: schedule.time_of_day ?? '03:00',
+        weekly_day: schedule.weekly_day ?? 7,
+      };
+    }
+  });
+
+  function scheduleHasChanges(): boolean {
+    if (!schedule) return false;
+    if (scheduleLocal.mode !== schedule.mode) return true;
+    switch (scheduleLocal.mode) {
+      case 'interval':
+        return scheduleLocal.interval_hours !== (schedule.interval_hours ?? -1);
+      case 'daily':
+        return scheduleLocal.time_of_day !== (schedule.time_of_day ?? '');
+      case 'weekly':
+        return scheduleLocal.time_of_day !== (schedule.time_of_day ?? '')
+            || scheduleLocal.weekly_day !== (schedule.weekly_day ?? -1);
+      default:
+        return false;
+    }
+  }
+
+  async function onSaveSchedule() {
+    scheduleSaving = true;
+    try {
+      const patch: { mode: ScanScheduleMode; interval_hours?: number; time_of_day?: string; weekly_day?: number } = {
+        mode: scheduleLocal.mode,
+      };
+      if (scheduleLocal.mode === 'interval') patch.interval_hours = scheduleLocal.interval_hours;
+      if (scheduleLocal.mode === 'daily' || scheduleLocal.mode === 'weekly') patch.time_of_day = scheduleLocal.time_of_day;
+      if (scheduleLocal.mode === 'weekly') patch.weekly_day = scheduleLocal.weekly_day;
+      await updateScanSchedule(patch);
+      await client.invalidateQueries({ queryKey: qk.scanSchedule() });
+    } catch (e) {
+      showToast(`Schedule save failed: ${(e as { code?: string })?.code ?? 'unknown'}`);
+    } finally {
+      scheduleSaving = false;
+    }
+  }
+
+  function formatRelative(iso: string): string {
+    const target = new Date(iso);
+    const now = new Date();
+    const diffMs = target.getTime() - now.getTime();
+    const absHours = Math.abs(diffMs) / 3_600_000;
+    let rel: string;
+    if (absHours < 1) {
+      const mins = Math.round(Math.abs(diffMs) / 60_000);
+      rel = diffMs >= 0 ? `in ${mins} min` : `${mins} min ago`;
+    } else if (absHours < 48) {
+      const h = Math.round(absHours);
+      rel = diffMs >= 0 ? `in ${h} hour${h === 1 ? '' : 's'}` : `${h} hour${h === 1 ? '' : 's'} ago`;
+    } else {
+      const days = Math.round(absHours / 24);
+      rel = diffMs >= 0 ? `in ${days} days` : `${days} days ago`;
+    }
+    const local = target.toLocaleString();
+    return `${rel} (${local})`;
+  }
+
   // ---- Cover art bulk refetch ----
   let bulkBusy = $state(false);
   let bulkResult = $state<string | null>(null);
@@ -430,6 +517,77 @@
     {/if}
   </section>
 
+  <!-- Scan schedule -->
+  <section class="rounded border border-border bg-surface p-4 space-y-3">
+    <div>
+      <h2 class="font-display text-lg font-medium">Scan schedule</h2>
+      <p class="mt-1 text-sm text-text-secondary">
+        Run a library scan automatically on a recurring cadence. Manual triggers
+        and boot scans are unaffected.
+      </p>
+    </div>
+
+    {#if schedule}
+      <div class="grid gap-3 sm:grid-cols-[auto_1fr] items-center">
+        <label class="text-sm text-text-secondary" for="schedule-mode">Mode</label>
+        <select id="schedule-mode" bind:value={scheduleLocal.mode}
+                class="text-sm rounded border border-border bg-background px-2 py-1">
+          <option value="off">Off</option>
+          <option value="interval">Every N hours</option>
+          <option value="daily">Daily at time</option>
+          <option value="weekly">Weekly at day + time</option>
+        </select>
+
+        {#if scheduleLocal.mode === 'interval'}
+          <label class="text-sm text-text-secondary" for="schedule-interval">Interval</label>
+          <div class="flex items-center gap-2">
+            <input id="schedule-interval" type="number" min="1" max="168"
+                   bind:value={scheduleLocal.interval_hours}
+                   class="w-20 text-sm rounded border border-border bg-background px-2 py-1" />
+            <span class="text-sm text-text-muted">hours</span>
+          </div>
+        {/if}
+
+        {#if scheduleLocal.mode === 'daily' || scheduleLocal.mode === 'weekly'}
+          <label class="text-sm text-text-secondary" for="schedule-time">Time</label>
+          <input id="schedule-time" type="time" bind:value={scheduleLocal.time_of_day}
+                 class="text-sm rounded border border-border bg-background px-2 py-1" />
+        {/if}
+
+        {#if scheduleLocal.mode === 'weekly'}
+          <label class="text-sm text-text-secondary" for="schedule-day">Day</label>
+          <select id="schedule-day" bind:value={scheduleLocal.weekly_day}
+                  class="text-sm rounded border border-border bg-background px-2 py-1">
+            <option value={1}>Monday</option>
+            <option value={2}>Tuesday</option>
+            <option value={3}>Wednesday</option>
+            <option value={4}>Thursday</option>
+            <option value={5}>Friday</option>
+            <option value={6}>Saturday</option>
+            <option value={7}>Sunday</option>
+          </select>
+        {/if}
+      </div>
+
+      <div class="flex items-center gap-3">
+        <button type="button" disabled={!scheduleHasChanges() || scheduleSaving}
+                onclick={onSaveSchedule}
+                class="rounded-md bg-action-primary px-4 py-2 text-sm font-medium text-action-fg hover:opacity-90 disabled:opacity-50">
+          {scheduleSaving ? 'Saving…' : 'Save changes'}
+        </button>
+        {#if schedule.next_scheduled_at}
+          <span class="text-xs text-text-muted">
+            Next scan: {formatRelative(schedule.next_scheduled_at)}
+          </span>
+        {:else if scheduleLocal.mode === 'off'}
+          <span class="text-xs text-text-muted">Schedule is off.</span>
+        {/if}
+      </div>
+    {:else}
+      <p class="text-sm text-text-muted">Loading…</p>
+    {/if}
+  </section>
+
   <!-- Cover art bulk refetch -->
   <section class="rounded border border-border bg-surface p-4">
     <h2 class="font-display text-lg font-medium">Cover art</h2>

web/src/routes/admin/admin.test.ts

@@ -41,7 +41,21 @@ vi.mock('$lib/api/admin', async () => {
     deleteQuarantineFile: vi.fn().mockResolvedValue({}),
     deleteQuarantineViaLidarr: vi.fn().mockResolvedValue({}),
     triggerScan: vi.fn().mockResolvedValue({}),
-    refetchMissingCovers: vi.fn().mockResolvedValue({ queued: 0 })
+    refetchMissingCovers: vi.fn().mockResolvedValue({ queued: 0 }),
+    createScanScheduleQuery: vi.fn(() =>
+      readable({
+        data: {
+          mode: 'off',
+          interval_hours: null,
+          time_of_day: null,
+          weekly_day: null,
+          next_scheduled_at: null,
+        },
+        isPending: false,
+        isError: false
+      })
+    ),
+    updateScanSchedule: vi.fn().mockResolvedValue({})
   };
 });
 
@@ -242,6 +256,14 @@ describe('admin Overview page', () => {
     );
   });
 
+  test('renders the scan-schedule section with mode=off default', () => {
+    setupOverview();
+    render(OverviewPage);
+    expect(screen.getByText('Scan schedule')).toBeInTheDocument();
+    const select = screen.getByLabelText('Mode') as HTMLSelectElement;
+    expect(select.value).toBe('off');
+  });
+
   test('Library scan card shows Processing badge when library tally is populated and in-flight', async () => {
     const { readable } = await import('svelte/store');
     (createScanStatusQuery as ReturnType<typeof vi.fn>).mockReturnValueOnce(