feat: add OAuth proxy support to eliminate CORS issues

Add server-side proxy endpoints for OAuth discovery, client registration,
and token exchange to avoid CORS issues when using proxy connection mode.

Server proxy endpoints:
- GET /oauth/resource-metadata - proxies OAuth protected resource metadata
- GET /oauth/metadata - proxies OAuth authorization server metadata
- POST /oauth/register - proxies dynamic client registration
- POST /oauth/token - proxies token exchange

Client changes:
- Construct correct RFC 9728/8414 path-aware well-known URLs client-side
- Route all OAuth discovery through proxy when in proxy connection mode
- Eliminate direct browser fetches that fail with CORS in proxy mode

package.json

@@ -69,7 +69,7 @@
     "jest-fixed-jsdom": "^0.0.9",
     "lint-staged": "^16.1.5",
     "playwright": "^1.56.1",
-    "prettier": "^3.7.1",
+    "prettier": "^3.7.4",
     "rimraf": "^6.0.1",
     "typescript": "^5.4.2"
   },