Local-only app: remove network, uploads, providers, backend, desktop

Phone is now a pure on-device recorder: no accounts, no servers, no
background uploads (INTERNET permission gone). File sync is the user's
own tooling; the library adopts externally added files.

Android:
- Delete provider package (Nextcloud, custom SHONAR, sync-folder,
  registry, auth, TOFU/TLS), sync stack (SyncWorker/Drain/Slots,
  MigrationRunner), provider/storage/folder UI, AI-via-server details.
- Home shows a fixed 'on this phone' library; details keep playback,
  rename, file info. Settings lose Network/provider/HTTP-logging.
- Library root is the stored folder or Music/Recordings; import is
  double-scan proof (mutex + unique filePath index, migration v3->v4
  dedupes by path) with regression tests.
- Drop okhttp/work/security-crypto/media deps; delete their tests.

Repo: backend/, desktop/, worker/, deploy/, shared/, server scripts
and docs removed; README rewritten; CI keeps the android job only.

docs/recording-consent.md

@@ -23,8 +23,9 @@ following the law where you are.
 - Provides an always-visible stop control on the recording screen and in the
   notification.
 - Has no remote-trigger recording capability of any kind.
-- Collects no telemetry and sends no data anywhere except the server URL you
-  configure.
+- Collects no telemetry and sends no data anywhere. There is no server,
+  no account, no network permission — recordings never leave the phone
+  except through file sync you set up yourself.
 
 ## Recommended practice