Add Python agent, WebSocket relay, real viewer, enrollment tokens

- WebSocket relay service (FastAPI) bridges agents and viewers
- Python agent with screen capture (mss), input control (pynput),
  script execution, and auto-reconnect
- Windows service wrapper, PyInstaller spec, NSIS installer for
  silent mass deployment (RemoteLink-Setup.exe /S /SERVER= /ENROLL=)
- Enrollment token system: admin generates tokens, agents self-register
- Real WebSocket viewer replaces simulated canvas
- Linux agent binary served from /downloads/remotelink-agent-linux
- DB migration 0002: viewer_token on sessions, enrollment_tokens table
- Sign-up pages cleaned up (invite-only redirect)

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

Dockerfile

@@ -13,7 +13,9 @@ COPY --from=deps /app/node_modules ./node_modules
 COPY . .
 
 ARG NEXT_PUBLIC_APP_URL=http://localhost:3000
+ARG NEXT_PUBLIC_RELAY_URL=localhost:8765
 ENV NEXT_PUBLIC_APP_URL=$NEXT_PUBLIC_APP_URL
+ENV NEXT_PUBLIC_RELAY_URL=$NEXT_PUBLIC_RELAY_URL
 ENV NEXT_TELEMETRY_DISABLED=1
 
 RUN pnpm build