Add Icon Toggle for Play/Pause Button

[AkshayAshokCode]

Replace the current “Start” and “Pause” buttons in the Pomodoro tool window with a single toggle button that switches between a Play icon and a Pause icon based on the timer state.

Scope:

Use icons like ▶️ and ⏸️ (use proper SVGs or JetBrains' recommended icons)
Handle the toggle based on PomodoroTimerService.state
Use TimerState.RUNNING, TimerState.PAUSED, and TimerState.IDLE for logic
Add tooltip (e.g., “Start Pomodoro”, “Pause Pomodoro”) for better accessibility