feat: Integrations splits into Library, Acquisition, Metadata sources and Email & network, each a page on the admin rail; the Overview keeps only what needs you (M503 #5607)

- Library: the folders, Run scan and a row per scan job, cover art, fingerprints and loudness (off the Overview and Duplicates)
- Acquisition: indexers and clients, searching, re-acquisition (off Missing files), Lidarr
- Metadata sources: AcoustID, and one provider block for cover art and tags in place of the pasted pair
- Email & network: outgoing email, the notification schedule, public address, proxies
- Lidarr, outgoing email and the provider block are rebuilt as SettingsGroup rows; failures read as sentences, not codes
- Duplicates and Missing files say what their setting is and link to where it is set

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

internal/server/server.go

@@ -161,7 +161,7 @@ func (s *Server) Router() http.Handler {
 		)
 		lidarrCfg := lidarrconfig.New(s.Pool)
 		// Per-call client factory: re-reads config so an admin save in
-		// /admin/integrations takes effect immediately without restart.
+		// Admin › Acquisition takes effect immediately without restart.
 		// Returns nil when Lidarr is disabled, which the Service-layer
 		// methods translate to ErrLidarrDisabled.
 		lidarrClientFn := func() *lidarr.Client {