feat: OAuth user fixes + dashboard UI improvements (v3.2.0)

- Bug A: Fix OAuth consent redirect loop (return_url path-relative)
- Bug B: Accept OAuth JWT tokens on /u/{user_id}/{alias}/mcp
- Bug C: Add user OAuth client CRUD (list/create/delete) + new page
- D-1: Sidebar border via Tailwind class, version footer in sidebar
- D-2: Remove broken setInterval targeting #stats-container
- D-3: 404.html purple primary colors + system dark mode support
- D-4: Fix invisible buttons (bg-gray-200 + text-white in light mode)
- D-5: Pin Alpine.js to 3.14.8, remove duplicate CSRF meta tag
- D-6: Fix invisible lang toggle button in settings (dark mode)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

core/oauth/client_registry.py

@@ -76,6 +76,7 @@ class ClientRegistry:
         grant_types: list[str] | None = None,
         allowed_scopes: list[str] | None = None,
         metadata: dict | None = None,
+        owner_user_id: str | None = None,
     ) -> tuple[str, str]:
         """
         Create new OAuth client.
@@ -99,6 +100,7 @@ class ClientRegistry:
             grant_types=grant_types or ["authorization_code", "refresh_token"],
             allowed_scopes=allowed_scopes or ["read", "write"],
             metadata=metadata or {},
+            owner_user_id=owner_user_id,
         )
 
         # Save