Add backup/restore, library sort, and PWA auto-update features

[EnesYilmazcode]

Summary

This PR adds three major features to Melody: backup/restore functionality for playlists and library metadata, persistent sort preferences in the Library view, and improved PWA auto-update detection for iOS. It also includes a hidden build readout accessible via long-press on the tab bar for debugging deployment state.

Key Changes

Backup & Restore

• Added exportBackup() and importBackup() functions to serialize/merge catalog and playlist data as JSON
• Backup exports include schema version and timestamp; restore validates schema and coerces fields to prevent crashes from hand-edited or foreign backups
• Restored tracks initially have no audio bytes; re-importing the same files reattaches them via the existing dedup match in addLocalTrack
• Playlists merge by name (appending unseen track IDs); tracks merge by ID with user state combined (play count, stars, last played)
• Added Export/Restore buttons in PlaylistsView with file picker and toast feedback

Library Sorting

• Added three sort modes: Recent (default, by dateAdded desc), Most Played (by playCount), and A–Z (alphabetical)
• Sort preference persists to localStorage with graceful fallback for private-mode Safari
• Refactored LibraryView to wrap filter and sort controls in a flex row that wraps on narrow screens
• Enhanced empty state with centered layout and NotesGlyph icon when library is empty

PWA Auto-Update & Build Readout

• Implemented registerServiceWorker() in new src/lib/pwa.js that explicitly checks for updates on a 1-hour interval and whenever the app returns to foreground (critical for iOS where PWA is frozen/resumed rather than reloaded)
• Added hidden VersionPeek component (long-press tab bar) showing commit hash and build timestamp, auto-hides after 5 seconds
• Build info injected at compile time via vite.config.js using git commit hash and timestamp
• Added Toast component for transient status messages (import summaries, restore results) positioned above the dock

Supporting Changes

• Updated summarize() in format.js to use "songs" terminology and added formatTotalDuration() for human-readable duration formatting (e.g., "2 hr 51 min")
• Enhanced PlaylistCard to display a 2×2 artwork mosaic and track count alongside playlist name
• Modified ImportButton to filter non-audio files from multi-select (handles a-Shell folder sweeps with .json/.txt sidecars) and surface results via app-wide toast
• Added UIProvider toast state management for centralized status messaging
• Removed inline .importnote CSS in favor of app-wide toast pattern
• Updated README with PWA auto-update and data safety documentation

Workflow Infrastructure

• Added .claude/workflows/ship.js: a multi-phase pipeline for shipping code changes (research fleet → sequential implementers → slop-check fleet → fresh review → fix loop)
• Added .claude/commands/ship.md documentation for the ship workflow

Notable Implementation Details

• Backup restore uses a Dexie transaction to atomically merge tracks and playlists, preventing partial imports on failure
• Dedup logic in addLocalTrack now distinguishes between restored rows (no blob) and duplicates (blob exists), allowing re-import to reattach bytes without counting as a duplicate
• Sort state uses a pure lazy initializer to avoid StrictMode double-render side effects
• Toast and VersionPeek auto-dismiss with configurable timeouts; clicking either dismisses immediately
• Service worker update check explicitly called on visibility change to work around iOS PWA freeze/resume behavior
• All new UI elements (backup buttons, toast, version peek) use existing design tokens and follow the repo's idiom for comment density and naming

https://claude.ai/code/session_01NBLkqNYmSgVYiTwUDcdogL