Feat/pomodoro

[TexasOct]

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Add Pomodoro timer feature that controls perception layer
(screenshot/keyboard/mouse capture) based on work sessions.
Implements an idle-by-default strategy where perception only runs
during active Pomodoro sessions.

Core Changes:

• Add PomodoroManager to handle session lifecycle and coordinate
  with perception layer
• Implement session database storage (pomodoro_sessions,
  raw_records tables)
• Create API handlers for starting/stopping Pomodoro sessions
• Add migration system with initial schemas and Pomodoro feature
  migration

Perception Layer:

• Remove _pomodoro_mode flag from ScreenshotCapture (Pomodoro
  only controls start/stop)
• Fix screenshot capture blocking issue by removing
  run_in_executor
• Simplify screenshot loop to call capture() directly in
  async context
• Improve timing accuracy by compensating for execution time
  in sleep

Architecture:

• Idle Mode (default): Perception layer stopped, zero resource
  usage
• Active Mode (Pomodoro): Perception layer running, captures
  activity data
• Session data persisted to database for deferred batch
  processing
• SessionAgent paused during Pomodoro, resumes after for
  activity aggregation

Frontend:

• Add PomodoroTimer component with start/stop controls
• Create pomodoro Zustand store for state management
• Add Tauri event handlers for Pomodoro processing events
• Add i18n translations for Pomodoro UI

Documentation:

• Update .project.md with Pomodoro mode principles and design
  rules
• Document that Pomodoro has no system configuration parameters
• Clarify that capture behavior (smart capture, deduplication)
  is not affected by Pomodoro mode

Technical Notes:

• macOS Core Graphics requires screenshot capture in main event
  loop context
• Thread pool execution causes 30s blocking on sct.grab() -
  resolved by direct async calls
• Loop timing controlled by asyncio.sleep() with execution time
  compensation

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Add dedicated Tauri event emitters for Pomodoro processing:

• emit_pomodoro_processing_progress: Progress updates
• emit_pomodoro_processing_complete: Completion notifications
• emit_pomodoro_processing_failed: Error notifications

Resolves all TODOs in pomodoro_manager.py by integrating with
the existing event system infrastructure.

@TexasOct