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/lib/api/error-copy.ts

@@ -0,0 +1,8 @@
+import errorCopyJson from '../styles/error-copy.json';
+
+export const ERROR_COPY: Readonly<Record<string, string>> = errorCopyJson;
+
+export function copyForCode(code: string | null | undefined): string {
+  if (!code) return ERROR_COPY.unknown ?? 'Something went wrong.';
+  return ERROR_COPY[code] ?? ERROR_COPY.unknown ?? 'Something went wrong.';
+}

web/src/lib/styles/error-copy.json

@@ -0,0 +1,16 @@
+{
+  "unknown": "Something went wrong.",
+  "unauthenticated": "Your session has ended. Please sign in again.",
+  "connection_refused": "Couldn't reach the server. Check the URL and try again.",
+  "lidarr_unreachable": "Lidarr is unreachable right now. Try again, or check Admin → Integrations.",
+  "lidarr_disabled": "Lidarr integration is not enabled.",
+  "lidarr_auth_failed": "Lidarr authentication failed.",
+  "lidarr_defaults_incomplete": "Lidarr is missing a default quality profile or root folder. Set them in Admin → Integrations.",
+  "lidarr_server_error": "Lidarr returned an error. Check Lidarr's logs for the cause.",
+  "lidarr_rejected": "Lidarr rejected the request. Check the server logs for the field-level reason.",
+  "lidarr_album_lookup_failed": "Lidarr doesn't recognize this album. Try Resolve or Delete file instead.",
+  "album_mbid_missing": "This track has no Lidarr album to remove.",
+  "request_not_pending": "This request is no longer pending.",
+  "request_not_found": "That request no longer exists.",
+  "track_not_found": "That track no longer exists."
+}