feat(app-update): add in-app update flow with auto-check and manual trigger

[j4rviscmd]

Summary

Add a complete in-app update flow for Scripta, including automatic update checks on startup and a manual "Check for Updates" option in Settings. The update dialog shows release notes rendered as Markdown, version comparison, download progress, and supports skip-version functionality.

Related Issue

N/A — No existing issue for this feature.

Type of Change

• ✨ New feature
• 💥 Breaking change
• 🐛 Bug fix
• 📝 Documentation
• ♻️ Refactoring
• 🔧 Chore

Key Changes

Update State Machine

• Pure useReducer with 8 states (idle, checking, available, downloading, installing, restarting, upToDate, error) and 9 actions
• Clean Architecture: domain logic separated from UI and infrastructure

UI (UpdateDialog)

• 7 view states with appropriate UI for each phase
• Markdown-rendered release notes via react-markdown
• Current vs available version display
• Download progress indicator
• Text selection enabled for release notes
• "View past releases" external link

Auto-Check on Startup

• Runs immediately on mount, waits for splash completion before showing dialog
• Silent on up-to-date or error (no dialog)
• Respects skipped versions (persisted via tauri-plugin-store)
• 10-second timeout for offline resilience

Manual Check (Settings)

• "Check for Updates" button in Settings dialog
• "Release Notes" external link
• Shows dialog immediately (no splash wait)

CI/CD

• New generate-notes job in release.yml using GitHub API generateReleaseNotes()
• Release notes passed as releaseBody to tauri-action

Infrastructure

• Added tauri-plugin-updater and tauri-plugin-process
• Added process:allow-restart capability
• Window focus on startup (window.set_focus())

Breaking Changes

None.

Test

• Run npm run dev and verify the app starts without errors
• Open Settings → confirm "Check for Updates" button appears
• Click "Check for Updates" → verify checking spinner, then result dialog
• Verify "Release Notes" link opens GitHub releases page
• Verify release notes are rendered as Markdown with proper formatting
• Verify text in release notes is selectable
• Disconnect network → Click "Check for Updates" → verify error dialog after timeout
• Build with cargo build → verify no compilation errors

Checklist

• Code follows clean architecture (proper separation of concerns)
• Code is simple and concise (no unnecessary complexity)
• Comments are sufficient for non-obvious logic
• No sensitive information included (credentials, secrets, personal data)
• Conventional Commits format followed in commit messages
• Tests added/updated (or N/A for docs/chore) — N/A (UI feature, requires Tauri runtime)