Fix/percistent mcp connection (#392)

* feat(oauth): add support for refresh tokens in OAuth flow and update database schema

* feat(prompts): add MCP prompts and corresponding functionality for prompt retrieval

* feat(auth): enhance error handling for refresh token operations and validation

supabase/migrations/20260505120000_api_keys_refresh_token.sql

@@ -0,0 +1,11 @@
+-- Add refresh_token_hash to api_keys for OAuth refresh-token grant support.
+-- OAuth-issued keys store a SHA-256 hashed refresh token here. Direct API
+-- keys (created via the settings UI) leave this column NULL.
+ALTER TABLE public.api_keys
+  ADD COLUMN refresh_token_hash text;
+
+CREATE UNIQUE INDEX idx_api_keys_refresh_token_hash
+  ON public.api_keys (refresh_token_hash)
+  WHERE refresh_token_hash IS NOT NULL;
+
+NOTIFY pgrst, 'reload schema';