feat: add proactive command monitors

[zhanba]

Summary

• add the standalone startMonitor tool with task-scoped monitor IDs, timeout/persistence controls, cancellation, and active-monitor environment context
• deliver batched, rate-limited monitor output events through CLI and VS Code transports into non-removable, steerable WebUI notifications
• preserve existing background executeCommand transcripts and durable completion notifications while preventing duplicate completion notifications for monitor jobs

Test plan

• Run bun check
• Run bun tsc
• Run common monitor watcher tests (14 passed)
• Run CLI background job manager tests (122 passed)
• Run WebUI chat toolbar tests (6 passed)
• Run VS Code extension tests (199 passed)
• Run pre-push unit test suite
• Run full VS Code integration suite (attempted twice; @vscode/test-electron timed out during startup after 15 seconds, before assertions)

Notes

• CLI monitor events consume stdout only while preserving stdout and stderr in the transcript.
• VS Code's TerminalShellExecution.read() exposes a combined stream, so its monitor events can include stderr.

🤖 Generated with Pochi

[codecov-commenter]

Codecov Report

❌ Patch coverage is 46.59207% with 525 lines in your changes missing coverage. Please review.
✅ Project coverage is 31.04%. Comparing base (2c6432d) to head (3cd44d0).

Files with missing lines	Patch %	Lines
...scode/src/integrations/monitor/monitor-registry.ts	0.00%	147 Missing ⚠️
packages/cli/src/task-runner.ts	0.00%	61 Missing ⚠️
packages/vscode/src/tools/monitor.ts	0.00%	53 Missing ⚠️
...de-webui/src/features/tools/components/monitor.tsx	17.07%	34 Missing ⚠️
...ebui/src/features/chat/components/chat-toolbar.tsx	13.51%	32 Missing ⚠️
packages/cli/src/tools/monitor.ts	11.76%	30 Missing ⚠️
...de-webui/src/components/message/monitor-events.tsx	14.28%	30 Missing ⚠️
packages/cli/src/lib/background-job-manager.ts	75.70%	26 Missing ⚠️
...ebui/src/features/chat/hooks/use-monitor-events.ts	44.73%	20 Missing and 1 partial ⚠️
...c/features/chat/lib/use-background-job-display.tsx	0.00%	16 Missing ⚠️
... and 13 more

❌ Your patch status has failed because the patch coverage (46.59%) is below the target coverage (75.00%). You can increase the patch coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1894      +/-   ##
==========================================
- Coverage   36.94%   31.04%   -5.91%     
==========================================
  Files         770      779       +9     
  Lines       81173    82120     +947     
  Branches     3697     4363     +666     
==========================================
- Hits        29990    25493    -4497     
- Misses      51070    56508    +5438     
- Partials      113      119       +6     

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