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/quarantine/+page.svelte

@@ -8,13 +8,14 @@
     deleteQuarantineViaLidarr
   } from '$lib/api/admin';
   import { qk } from '$lib/api/queries';
+  import { copyForCode } from '$lib/api/error-copy';
   import { playRadio } from '$lib/player/store.svelte';
   import type { AdminQuarantineRow, LidarrQuarantineReason } from '$lib/api/types';
 
   // Aggregated triage queue. One row per track, with per-row resolution
   // actions: Resolve (clears reports), Delete file (Bronze; modal-confirm),
   // Delete via Lidarr (Oxblood; typed-confirm "DELETE"). Mirrors
-  // /admin/requests for shape — toast helper, errorCopy(), invalidateQueries.
+  // /admin/requests for shape — toast helper, copyForCode(), invalidateQueries.
 
   const client = useQueryClient();
 
@@ -78,23 +79,6 @@
     }, 5000);
   }
 
-  function errorCopy(code: string): string {
-    switch (code) {
-      case 'lidarr_unreachable':
-        return "Lidarr is unreachable right now. Try again, or check Settings → Integrations.";
-      case 'lidarr_disabled':
-        return 'Lidarr integration is not enabled.';
-      case 'lidarr_auth_failed':
-        return 'Lidarr authentication failed.';
-      case 'lidarr_album_lookup_failed':
-        return "Lidarr doesn't recognize this album. Try Resolve or Delete file instead.";
-      case 'album_mbid_missing':
-        return 'This track has no Lidarr album to remove.';
-      default:
-        return "Couldn't reach Lidarr.";
-    }
-  }
-
   async function invalidate() {
     await client.invalidateQueries({ queryKey: qk.adminQuarantine() });
   }
@@ -105,7 +89,7 @@
       await invalidate();
     } catch (e) {
       const code = (e as { code?: string }).code ?? 'unknown';
-      showToast(errorCopy(code));
+      showToast(copyForCode(code));
     }
   }
 
@@ -124,7 +108,7 @@
       await invalidate();
     } catch (e) {
       const code = (e as { code?: string }).code ?? 'unknown';
-      showToast(errorCopy(code));
+      showToast(copyForCode(code));
     }
   }
 
@@ -153,9 +137,9 @@
       const code = (e as { code?: string }).code ?? 'unknown';
       // Inline error keeps the modal open so the operator sees the failure
       // alongside the album they were about to remove.
-      deleteLidarrError = errorCopy(code);
+      deleteLidarrError = copyForCode(code);
       // Also surface as toast so it's visible after dismissing the modal.
-      showToast(errorCopy(code));
+      showToast(copyForCode(code));
     }
   }