feat(mcp): add Streamable HTTP transport with OAuth 2.0 (#1033)

* feat(mcp): add Streamable HTTP transport with OAuth 2.0

  Odysseus could only reach MCP servers over stdio and SSE, so modern
  remote servers like https://mcp.higgsfield.ai/mcp (Streamable HTTP,
  gated behind OAuth) could not be connected.

  Add an `http` transport that connects via the SDK's
  streamablehttp_client and authenticates with the SDK's
  OAuthClientProvider: RFC 9728 protected-resource discovery, RFC 8414
  authorization-server metadata, Dynamic Client Registration,
  authorization-code + PKCE, and token refresh. A small bridge
  (src/mcp_oauth.py) connects the SDK's blocking callback to the existing
  web callback route via an asyncio.Future keyed by the OAuth `state`,
  and the dynamic client registration plus tokens persist per-server in a
  new encrypted `oauth_tokens` column.

  The connect runs as a bounded background task so the "Add server"
  request returns immediately; redirect_handler publishes needs_auth +
  auth_url to connection state as soon as discovery/DCR completes (which
  can exceed the bounded wait), and the UI polls until connected. Remote
  users finish via the existing paste-back flow. The Google OAuth path is
  left unchanged.

  - core/database.py: encrypted oauth_tokens column + migration
  - src/mcp_oauth.py: OAuth provider, DB-backed TokenStorage, state registry
  - src/mcp_manager.py: http dispatch, background connect, _connect_http
  - routes/mcp_routes.py: http validation, needs_auth/auth_url, callback bridge
  - static/js/settings.js: Streamable HTTP option + OAuth flow with polling
  - tests: 5 new unit tests (transport dispatch, registry, token storage)

  Verified against the live Higgsfield server: discovery, DCR (client_id
  issued), loopback redirect accepted, and a PKCE authorization URL with
  needs_auth status. No regressions (full suite delta is only the 5 added
  passing tests).

* fix(mcp): address PR #1033 review feedback

  - mcp_oauth: derive redirect URI from OAUTH_REDIRECT_BASE_URL/APP_PUBLIC_URL
    (default http://localhost:7000) instead of hardcoding the port
  - mcp_oauth: leave OAuth scope unset so the SDK derives it from the server's
    WWW-Authenticate/protected-resource metadata; hardcoding an OIDC scope broke
    non-OpenID MCP servers (verified: Higgsfield still gets its server-derived
    scope)
  - mcp_oauth: prune abandoned OAuth flows (_prune_stale + _pending_ts) so the
    module-level registries can't grow unbounded
  - mcp_oauth: persist tokens/client-info in a single DB session/commit
    (_update) instead of a load+save double round-trip
  - mcp_manager: cancel and drop the background connect task in
    disconnect_server so a deleted server stops publishing status
  - database: document why the oauth_tokens migration uses TEXT while the model
    declares EncryptedText (encryption is applied at the Python layer)
  - settings.js: surface persistent OAuth-poll failures and an explicit timeout
    message instead of silently swallowing errors
  - tests: cover the stale-flow pruning

* static/js/settings.js now shows an in-flight loading state on the buttons that fire requests:

tests/test_mcp_manager.py

@@ -1,4 +1,7 @@
-from src.mcp_manager import _format_mcp_connection_error
+import asyncio
+from unittest.mock import patch
+
+from src.mcp_manager import _format_mcp_connection_error, McpManager
 
 
 def test_playwright_mcp_connection_error_includes_install_hint():
@@ -24,3 +27,15 @@ def test_generic_mcp_connection_error_preserves_original_error():
     )
 
     assert msg == "boom"
+
+
+def test_http_transport_routes_to_start_http_connect():
+    mgr = McpManager()
+
+    async def fake_start(server_id, name, url):
+        return "ROUTED"
+
+    with patch.object(McpManager, "_start_http_connect", side_effect=fake_start) as m:
+        result = asyncio.run(mgr.connect_server("id1", "n", "http", url="https://x/mcp"))
+    assert result == "ROUTED"
+    m.assert_called_once()