Fix Foundry auth: migrate to Better Auth adapter, fix access token retrieval

- Remove @ts-nocheck from better-auth.ts, auth-user/index.ts, app-shell.ts
  and fix all type errors
- Fix getAccessTokenForSession: read GitHub token directly from account
  record instead of calling Better Auth's internal /get-access-token
  endpoint which returns 403 on server-side calls
- Re-implement workspaceAuth helper functions (workspaceAuthColumn,
  normalizeAuthValue, workspaceAuthClause, workspaceAuthWhere) that were
  accidentally deleted
- Remove all retry logic (withRetries, isRetryableAppActorError)
- Implement CORS origin allowlist from configured environment
- Document cachedAppWorkspace singleton pattern
- Add inline org sync fallback in buildAppSnapshot for post-OAuth flow
- Add no-retry rule to CLAUDE.md

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

foundry/compose.dev.yaml

@@ -41,6 +41,7 @@ services:
       HF_DAYTONA_ENDPOINT: "${HF_DAYTONA_ENDPOINT:-}"
       HF_DAYTONA_API_KEY: "${HF_DAYTONA_API_KEY:-}"
     ports:
+      - "6420:6420"
       - "7741:7741"
     volumes:
       - "..:/app"