feat: add Pomodoro Timer web app with background audio notifications

[key1989han]

Summary

Implemented a minimal Pomodoro Timer web app as a single HTML page with reliable background audio notifications.

Features

Core Functionality

• ✅ Single HTML page with configurable timer input (minutes)
• ✅ Timer display showing MM:SS format countdown
• ✅ Start/pause/reset button controls
• ✅ When timer reaches 00:00: stops, plays notification sound, resets display back to original configured time
• ✅ Single repeating timer (no pomodoro cycle tracking)

Background Audio (Critical Requirement)

• ✅ Uses Web Audio API for notification sound generation
• ✅ Works even when Chrome tab is in background or minimized
• ✅ Handles browser audio restrictions (AudioContext resume on user interaction)
• ✅ Pleasant chime sound using multiple frequencies (C5, E5, G5, C6)

Interface

• ✅ Minimal design: timer input field, timer display, and start/pause/reset buttons
• ✅ Clean, functional layout with gradient background
• ✅ No external dependencies - pure HTML/CSS/JS
• ✅ Responsive design

Technical Implementation

• Audio: Web Audio API with oscillator nodes for sound generation
• Timer: setInterval with proper cleanup on pause/reset
• State: Simple JavaScript state management
• Styling: CSS with glassmorphism effect

Testing

1. Open pomodoro-timer.html in Chrome
2. Set timer to 1 minute for quick testing
3. Click Start
4. Minimize Chrome or switch to another tab
5. Wait for timer to complete
6. Verify notification sound plays even in background

Files Added

• pomodoro-timer.html - Complete Pomodoro Timer web app

Fixes #1