Connections own their credentials

Migration 0038 moves every stored secret (OAuth tokens, MCP OAuth
tokens and client registrations, API keys) into the connection's
encrypted envelope, links API-key tools to one connection per distinct
credential, allows several accounts per provider, and adds
credential_mode to sources and tools. OAuth MCP tools keep resolving
each member's own token, as they did before.

docsgpt.connectors.service is now the only reader of OAuth tokens:
get_valid_token_info refreshes under a row lock and persists rotated
refresh tokens, and a revoked grant flags the connection, pauses its
sources and notifies the owner. Loaders build from a connection
(BaseConnectorLoader.from_connection), so scheduled sync covers Drive,
SharePoint and Confluence sources with no browser. S3 and Reddit keys
stay on the connection instead of in remote_data.

New endpoints: POST /api/connections, /setup, /reconnect,
/picker-token, /claim, DELETE /api/connections/<id>, per-action
permissions and MCP refresh-tools. Upload, file listing, sync and
validate-session take a connection_id; session tokens keep working for
this release. The tool executor reads credentials from the resolved
connection (owner or member mode) and pauses on a Connect card when a
connection needs signing in. docsgpt connectors reencrypt rewrites
stored credentials after a key rotation.

tests/worker/test_remote_worker.py

@@ -125,7 +125,8 @@ class TestSyncWorker:
         captured: list[dict] = []
 
         def _fake_sync(self, source_data, name_job, user, loader,
-                       sync_frequency, retriever, doc_id=None, directory="temp"):
+                       sync_frequency, retriever, doc_id=None, directory="temp",
+                       connection_id=None):
             captured.append({
                 "name_job": name_job,
                 "user": user,