Wire frontend to the backend: auth, organizations, real patient API

Connects the UI-only app to the new backend over Better Auth + a small
patient API client, replacing the in-memory fixture and placeholder identity.

- Better Auth React client (lib/auth-client.ts) + shared access-control
  roles; API client (lib/api-client.ts) sending credentials cross-origin.
- Designed (auth) route group: login, signup, verify-email, forgot/reset
  password, clinic onboarding, and accept-invite.
- proxy.ts (this Next's renamed middleware) optimistic redirect + an
  authoritative client AppAuthGuard requiring a session and active clinic.
- Real identity in nav-user (useSession + sign out); the unused team
  switcher repurposed as an organization (clinic) switcher; Care-team
  settings tab manages members and invitations.
- lib/patients.ts now calls the org-scoped API (types unchanged); patients
  table and create/edit dialog updated for async create/update.
- next.config: standalone output + Dockerfile for containerized runs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/package.json

@@ -19,6 +19,7 @@
     "@xyflow/react": "^12.10.2",
     "ai": "^6.0.193",
     "ansi-to-react": "^6.2.6",
+    "better-auth": "^1.6.13",
     "class-variance-authority": "^0.7.1",
     "clsx": "^2.1.1",
     "cmdk": "^1.1.1",