🛜 feat: Support Legacy OAuth Servers without .well-known Metadata (#10917)

Adds support for MCP servers like StackOverflow that use OAuth but don't
provide standard discovery metadata at .well-known endpoints.

Changes:
- Add fallback OAuth endpoints (/authorize, /token, /register) when
  discoverAuthorizationServerMetadata returns undefined
- Add POST fallback in OAuth detection when HEAD returns non-401
  (StackOverflow returns 405 for HEAD, 401 for POST)
- Detect OAuth requirement from WWW-Authenticate: Bearer header even
  without resource_metadata URL
- Add fallback /token endpoint for token refresh when metadata
  discovery fails
- Add registration_endpoint to OAuthMetadata type

This mirrors the MCP SDK's behavior where it gracefully falls back to
default OAuth endpoint paths when .well-known metadata isn't available.

Tests:
- Add unit tests for detectOAuth.ts (POST fallback, Bearer detection)
- Add unit tests for handler.ts (fallback metadata, fallback refresh)
- Add StackOverflow to integration test servers

Fixes OAuth flow for servers that:
- Return 405 for HEAD requests (only support POST)
- Return 401 with simple "Bearer" in WWW-Authenticate
- Don't have .well-known/oauth-authorization-server endpoint
- Use standard /authorize, /token, /register paths

packages/data-provider/src/types/queries.ts

@@ -185,8 +185,8 @@ export interface MCPConnectionStatusResponse {
 export interface MCPServerConnectionStatusResponse {
   success: boolean;
   serverName: string;
-  connectionStatus: string;
   requiresOAuth: boolean;
+  connectionStatus: 'disconnected' | 'connecting' | 'connected' | 'error';
 }
 
 export interface MCPAuthValuesResponse {