feat(server,frontend): real-time sync architecture with message accumulator

- Add message-accumulator.js: cascades diff-based message accumulation
- Add 3-second cascade polling with broadcastToAll (was undefined!)
- Add /api/bridge/approve endpoint: tries accept/reject Step→Command→Terminal
- Add persistent approve/reject buttons in chat header toolbar
- Frontend: loadSessionMessages (trajectory + accumulated), applyNewMessages (WS push)
- Status change detection: _prevStatusKey tracking prevents unnecessary re-renders
- actionInProgress flag prevents DOM replacement during button fetch
- Known issues: Trajectory 341 hard limit, Cascade no command-approval state

.agents/AGENT.md

@@ -19,6 +19,10 @@ description: 모든 작업에 자동 적용되는 에이전트 행동 규칙.
 7. NEVER truncate error messages — always show the full error output
 8. NEVER use `curl` in PowerShell — always use `curl.exe`
 9. NEVER run `npm` directly — use `cmd /c npm` to avoid execution policy issues
+10. NEVER run `python` directly — use `C:\ProgramData\miniforge3\envs\gravity_web\python.exe`
+11. NEVER use `python -c "..."` inline one-liners in PowerShell — write a `.py` file instead
+12. NEVER start server without killing existing port process first (EADDRINUSE)
+13. NEVER use `send_command_input Terminate` to stop servers — use `Stop-Process` or `taskkill /F` via `run_command` instead (Terminate hangs the agent)
 
 ## ALWAYS (필수)