feat: in-app auto-update with notification badge

[khaira777]

Goal

Enable silent background downloads with an in-app notification badge across all platforms. Replace native OS dialogs with a subtle UI indicator. Enable Linux auto-update (currently disabled).

Design doc: in-app-updates-design.md

What Changes

Area	Before	After
Download trigger	User clicks "Download" in native dialog	Silent, automatic
Download progress	Console only	IPC → renderer badge shows %
Update ready	Native dialog	In-app badge with dropdown
Linux (AppImage)	Skipped	Works via electron-updater
Linux (deb/snap)	Skipped	Package manager (unchanged)
Store builds (MAS, MSIX)	Skipped	Still skipped
Dev mode	Skipped	Still skipped

Tasks

Task 1: Main process — silent download + Linux

File:

• Enable autoUpdater.autoDownload = true
• Remove download confirmation dialog (update-available handler)
• Remove restart confirmation dialog (update-downloaded handler)
• Add granular progress IPC channel (update-download-progress)
• Enable Linux: remove if (process.platform === 'linux') return;
• Linux non-AppImage: send linux-managed status, skip self-update
• Enable auto-updater initialization on Linux (!isStoreBuild only)
• Add restart-and-install IPC handler

Task 2: Preload — expose new IPC channels

File: main/preload.ts

• Add restartAndInstall invoke handler
• Add onUpdateProgress listener
• Add onUpdateReady listener

Task 3: Frontend — notification badge component

File: frontend/

• useUpdateStatus() hook — manages state from IPC events
• <UpdateBadge /> component — shows in app header
  • Hidden when idle/up-to-date
  • "↓ {percent}%" pill when downloading
  • Pulsing dot when ready
  • Dropdown with version + "Restart Now" / "Later"
• Location: POS topbar (visible to all users, not just settings)

Task 4: Cross-platform testing

Must verify ALL applicable platforms:

Platform	Format	Test
macOS	DMG (x64)	Silent download → badge → restart installs
macOS	DMG (arm64)	Same on Apple Silicon
macOS	MAS	Auto-update skipped (store status)
Windows	NSIS (x64)	Silent download → badge → restart installs
Windows	MSIX	Auto-update skipped (store status)
Linux	AppImage	Download → badge → restart
Linux	deb	"linux-managed" status, no errors
Linux	snap	Snap own update handles it
All	Dev mode	"dev-mode" status, no check
All	No internet	Check fails silently, no error UI

Edge cases:

• Download interrupted → retry works
• "Restart Now" disabled during download
• No active orders check before restart (POS safety)

Acceptance Criteria

• macOS + Windows: existing users get silent download on next launch
• Linux AppImage: first-time auto-update works
• Linux deb/snap: no noise, package manager handles updates
• Store builds: still skipped (MAS, MSIX)
• Badge is subtle, non-intrusive (24-32px)
• No native OS dialogs shown to user
• All platform tests pass

Out of Scope (future)

• Deferral ("remind me later", skip version)
• Restart safety check (no active orders)
• Changelog panel / "what's new" modal
• Delta updates, staged rollouts