web: shared note actions, reminder chips, page header, formatters and settings seam

From the audit (#5179, web half).

- NoteActions: share, pin, archive and trash (restore and delete forever
  when trashed), as both the card and the editor offer them. The editor's
  history toggle goes in its slot, and it closes on `acted`.
- ReminderActions: the Done / 1h / 1d chips on the card and in the editor,
  which are now the same chips.
- PageHeader: the back-to-board header that Settings, Sync and Linked
  devices each wrote out, now with a `back` icon from the shared set.
- notes/datetime: formatShortDateTime (was formatReminder and the editor's
  revLabel) and formatDateTime (the two `fmt` copies).
- notes/colors: labelDotClasses (the sidebar's and the tag manager's
  labelDot).
- Drawer links use exact-active-class instead of route.name ternaries.
- BoardView binds its three grids from one gridBinds object.
- Settings goes through repo.settings (rest, plus a local adapter that
  answers "needs a server") and shows load failures through AsyncState.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/src/views/SyncView.vue

@@ -4,6 +4,7 @@ import { useUiStore } from "../stores/ui";
 import BaseButton from "../components/BaseButton.vue";
 import BaseInput from "../components/BaseInput.vue";
 import Icon from "../components/Icon.vue";
+import PageHeader from "../components/PageHeader.vue";
 import DesktopMenuEntry from "../components/DesktopMenuEntry.vue";
 import {
   SUGGESTED_CAPTURE_SHORTCUT,
@@ -22,6 +23,7 @@ import {
   type UpdateStatus,
 } from "../desktop/bridge";
 import { errorMessage } from "../api/errors";
+import { formatDateTime } from "../notes/datetime";
 
 // Opt-in server sync for the desktop app. Being UNLINKED is the normal resting
 // state, not an incomplete setup — the app is local-first and fully usable having
@@ -309,11 +311,6 @@ async function disconnect() {
   }
 }
 
-function fmt(iso: string | null): string {
-  if (!iso) return "never";
-  return new Date(iso).toLocaleString();
-}
-
 // A background cycle finished — redraw from it, so this screen is never staler
 // than the board behind it.
 let stopSyncListener: (() => void) | null = null;
@@ -335,23 +332,7 @@ onBeforeUnmount(() => stopSyncListener?.());
 
 <template>
   <div class="mx-auto min-h-full max-w-2xl px-4 py-8">
-    <header class="mb-8 flex items-center gap-3">
-      <RouterLink to="/" class="icon-btn" title="Back to board" aria-label="Back to board">
-        <svg
-          class="h-[18px] w-[18px]"
-          viewBox="0 0 24 24"
-          fill="none"
-          stroke="currentColor"
-          stroke-width="2"
-          stroke-linecap="round"
-          stroke-linejoin="round"
-          aria-hidden="true"
-        >
-          <path d="m15 18-6-6 6-6" />
-        </svg>
-      </RouterLink>
-      <h1 class="text-xl font-bold tracking-tight">Sync</h1>
-    </header>
+    <PageHeader title="Sync" />
 
     <div v-if="loading" class="py-10 text-center text-sm text-neutral-400">Loading…</div>
 
@@ -366,7 +347,7 @@ onBeforeUnmount(() => stopSyncListener?.());
             </p>
             <p v-if="linkedAs" class="mt-0.5 text-xs text-neutral-400">as {{ linkedAs }}</p>
             <p class="mt-1 text-xs text-neutral-400">
-              Last synced {{ fmt(status?.last_sync_at ?? null) }}
+              Last synced {{ formatDateTime(status?.last_sync_at ?? null) }}
               <span v-if="pending"> · unsent changes on this device</span>
             </p>
             <p class="mt-0.5 text-xs text-neutral-400">