Add onSessionStart and duringSession hooks

[ayrtmn]

Summary

This PR adds comprehensive sound support to pomo with seamless audio playback inspired by TomatoBar:

1. New Hooks: onSessionStart and duringSession

Two new hook types for audio feedback:

• onSessionStart: Play sound when session starts (windup.wav)
• duringSession: Loop ambient sound during session (ticking.wav at 80% volume)

Both global (top-level) and per-task hooks are supported. Per-task hooks override global hooks.

2. Gapless Audio Playback

Uses mpv with --gapless-audio flag for seamless looping without gaps between iterations. Volume defaulted to 80% for better focus.

3. Audio Controls

• Space bar: Pauses/resumes both timer AND audio together
• "a" key: Toggles audio independently while timer keeps running
• Audio mute state persists - pressing space after muting via "a" only resumes timer
• "a" button disabled when session is paused

4. Command-line Audio Override

New --url / -u flag to override duringSession audio URL without editing config:

pomo -u "https://youtube.com/watch?v=..."  # Custom YouTube/Spotify audio

5. Timer Accuracy Fixes

Fixed timer drift issues when pausing/resuming multiple times by properly tracking elapsed time with pausedElapsed field.

Configuration

# Global hooks (defaults)
onSessionEnd: "ask"

onSessionStart:
  - [afplay, ~/sounds/windup.wav]

duringSession:
  - ["mpv", "--no-video", "--gapless-audio", "--loop-file=inf", "--volume=80", "~/sounds/ticking.wav"]

# Per-task hooks (override global)
work:
  duration: 25m
  onStart:
    - [afplay, ~/sounds/work-start.wav]  # overrides global
  during:
    - ["mpv", "--no-video", "--volume=80", "~/sounds/other.wav"]  # overrides global
  then:
    - [afplay, ~/sounds/ding.wav]

break:
  duration: 5m
  then:
    - [afplay, ~/sounds/ding.wav]

# Command-line override
# pomo -u "https://youtube.com/watch?v=..."

Sound Files

Copy sound files from TomatoBar or use your own:

mkdir -p ~/sounds
# Recommended from TomatoBar:
# - windup.wav (session start)
# - ticking.wav (during session - gapless loop)
# - ding.wav (session complete)

Key Bindings

Key	Action
Space	Pause/Resume timer AND audio together
a	Toggle audio only (timer keeps running)
p	Same as Space (pause/resume)
q	Quit session
s	Skip to next session
+ / Up	Increase duration
- / Down	Decrease duration
r	Reset session

Implementation

• config/config.go: Added OnSessionStart, DuringSession fields with mpv defaults
• sound/sound.go: Enhanced PlayCommandLoop to support both afplay and mpv with IPC for pause/resume
• ui/model.go: Audio state tracking (audioMuted, pausedElapsed)
• ui/handlers.go: Integrated hooks with proper cleanup, pause/resume synchronization
• cmd/root.go: Added --url flag
• cmd/runner.go: URL override logic

Testing

• Start sound (windup.wav) plays on session begin
• Ambient sound (ticking.wav) loops gapless during session at 80% volume
• Sounds properly cancelled on session end/quit
• Space pauses both timer and audio synchronously
• "a" toggles audio independently
• Audio mute persists across space presses
• "a" disabled when session is paused
• Timer remains accurate through multiple pause/resume cycles
• --url flag overrides config audio for YouTube/Spotify streams