refactor(web): consolidate error-copy table to JSON source of truth

Three admin pages had divergent inline error-code → user-copy switch
tables (with wording drift, including a stale "Settings → Integrations"
that should have been Admin). Consolidate into web/src/lib/styles/error-copy.json,
expose via web/src/lib/api/error-copy.ts (ERROR_COPY + copyForCode),
and refactor the three pages to import the helper.

Fixes the three-way drift; the only user-visible behavior change is
the quarantine page now correctly says "Admin → Integrations".

Sets up the JSON for the M7 Flutter client (#356) to consume the same
table.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

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

@@ -12,6 +12,7 @@
     deleteQuarantineViaLidarr
   } from '$lib/api/admin';
   import { qk } from '$lib/api/queries';
+  import { copyForCode } from '$lib/api/error-copy';
   import type {
     AdminQuarantineRow,
     LidarrRequest,
@@ -60,21 +61,6 @@
     toastTimer = setTimeout(() => { toast = null; }, 5000);
   }
 
-  function errorCopy(code: string): string {
-    switch (code) {
-      case 'lidarr_unreachable':           return "Lidarr is unreachable. Try again, or check Admin → Integrations.";
-      case 'lidarr_disabled':              return 'Lidarr integration is not enabled.';
-      case 'lidarr_auth_failed':           return 'Lidarr authentication failed.';
-      case 'lidarr_defaults_incomplete':   return 'Lidarr defaults missing — set them in Admin → Integrations.';
-      case 'lidarr_server_error':          return "Lidarr returned an error. Check Lidarr's logs.";
-      case 'lidarr_rejected':              return 'Lidarr rejected the request. Check the server logs for details.';
-      case 'request_not_pending':          return 'This request is no longer pending.';
-      case 'request_not_found':            return 'That request no longer exists.';
-      case 'track_not_found':              return 'That track no longer exists.';
-      default:                             return code || 'Action failed.';
-    }
-  }
-
   // ---- Two-click destructive confirm for quarantine actions ----
   // Map key is `${trackId}:${actionKey}`. First click sets a key; second
   // click within 3s fires the action; otherwise the key clears.
@@ -134,7 +120,7 @@
       await approveRequest(r.id);
       await invalidateRequests();
     } catch (e) {
-      showToast(errorCopy((e as { code?: string }).code ?? ''));
+      showToast(copyForCode((e as { code?: string }).code));
     }
   }
   async function onReject(r: LidarrRequest) {
@@ -142,7 +128,7 @@
       await rejectRequest(r.id);
       await invalidateRequests();
     } catch (e) {
-      showToast(errorCopy((e as { code?: string }).code ?? ''));
+      showToast(copyForCode((e as { code?: string }).code));
     }
   }
 
@@ -158,7 +144,7 @@
       await resolveQuarantine(row.track_id);
       await invalidateQuarantine();
     } catch (e) {
-      showToast(errorCopy((e as { code?: string }).code ?? ''));
+      showToast(copyForCode((e as { code?: string }).code));
     }
   }
   async function onDeleteFile(row: AdminQuarantineRow) {
@@ -172,7 +158,7 @@
       await deleteQuarantineFile(row.track_id);
       await invalidateQuarantine();
     } catch (e) {
-      showToast(errorCopy((e as { code?: string }).code ?? ''));
+      showToast(copyForCode((e as { code?: string }).code));
     }
   }
   async function onDeleteLidarr(row: AdminQuarantineRow) {
@@ -186,7 +172,7 @@
       await deleteQuarantineViaLidarr(row.track_id);
       await invalidateQuarantine();
     } catch (e) {
-      showToast(errorCopy((e as { code?: string }).code ?? ''));
+      showToast(copyForCode((e as { code?: string }).code));
     }
   }
 </script>