🛜 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

api/server/routes/mcp.js

@@ -429,13 +429,23 @@ router.get('/connection/status', requireJwtAuth, async (req, res) => {
     const connectionStatus = {};
 
     for (const [serverName] of Object.entries(mcpConfig)) {
-      connectionStatus[serverName] = await getServerConnectionStatus(
-        user.id,
-        serverName,
-        appConnections,
-        userConnections,
-        oauthServers,
-      );
+      try {
+        connectionStatus[serverName] = await getServerConnectionStatus(
+          user.id,
+          serverName,
+          appConnections,
+          userConnections,
+          oauthServers,
+        );
+      } catch (error) {
+        const message = `Failed to get status for server "${serverName}"`;
+        logger.error(`[MCP Connection Status] ${message},`, error);
+        connectionStatus[serverName] = {
+          connectionState: 'error',
+          requiresOAuth: oauthServers.has(serverName),
+          error: message,
+        };
+      }
     }
 
     res.json({