feat(mcp): OAuth per-user connectors (§15) — providers, PKCE copy-paste flow, env credential delivery

- oauth_providers registry table (per-provider client creds) + db/oauth_providers.rs
- mcp/oauth.rs: authorization-code + PKCE S256, RAM-only TTL'd flow store, copy-paste consent
- mcp/install.rs + verify.rs: connector file install + manifest verification
- activate persists a pending row (needs_oauth); /mcp/oauth/start + /complete exchange code for refresh token
- credential delivery via env var on docker exec (google_authorized_user JSON), never on disk
- mcp_catalog/mcp_user_servers: additive OAuth columns (ensure_column), catalog_name/oauth_provider/deliver_json bare TEXT snapshots
- frontend: connector-detail.js (OAuth login panel), shared/connector-common.js, connectors.js admin Sign-in providers modal
- API: /mcp/providers (admin OAuth creds), /mcp/oauth/start|complete
- .gitignore: add /homes/ (instance data), /connectors/, /reset.sh; drop stale /secrets/

web/css/page-shell.css

@@ -74,6 +74,7 @@ file-viewer-page {
 users-page,
 roles-page,
 connectors-page,
+connector-detail-page,
 marketplace-page,
 catalog-page,
 profile-page {