fix(api): Add automatic token refresh on 401 errors in GoCardless service.

- Add _make_authenticated_request helper that automatically handles 401 errors
- Clear token cache and retry once when encountering expired tokens
- Refactor all API methods to use centralized request handling
- Fix banks API to properly handle institutions response structure
- Eliminates need for container restarts when tokens expire

🤖 Generated with [Claude Code](https://claude.ai/code)

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

leggen/api/routes/banks.py

@@ -32,7 +32,7 @@ async def get_bank_institutions(
                 countries=inst["countries"],
                 logo=inst.get("logo"),
             )
-            for inst in institutions_data
+            for inst in institutions_data.get("results", [])
         ]
 
         return APIResponse(