Add update-available badge to system tray icon

[niels9001]

When an update is available (readyToDownload or readyToInstall), the tray icon switches to a badged variant with an orange dot. Works for both default mode (color icon.ico) and theme-adaptive mode (light/dark variants).

Changes

Tray icon update badge

• Add 3 badged icon variants
• Extend get_icon() to select badged variant based on update_available state
• Add set_tray_icon_update_available() for runtime icon switching
• Hook into UpdateUtils.cpp state transitions via dispatch_run_on_main_ui_thread
• Check UpdateState at startup to show badge immediately if update pending
• Add 'Update available' context menu item at top of tray menu when active

Fix: update icons not deployed (bug fix)

• Add APPICON_UPDATE icon resource to runner.base.rc (iconUpdate.ico was missing)
• Add CopyFileToFolders entries for iconUpdate.ico, PowerToysDarkUpdate.ico, and PowerToysWhiteUpdate.ico in runner.vcxproj
• Add all update icon files to installer Core.wxs so they ship in releases

UX improvements

• 'Update available' tray menu item now navigates to General page (Overview) instead of opening Settings to Dashboard
• Update InfoBar severity changed from Success/Informational to Warning across GeneralPage, LaunchPage, and CheckUpdateControl
• Dashboard update badge gradient and icon refreshed (orange theme, exclamation glyph)
• AccentButtonStyle applied to 'Install Now' button
• Fixed casing: 'Update Available' to 'Update available'
• Added UpdateAvailableInfoBar.Title resource string
• Add orange update dot to the General navview item

Screenshots

Before:

After:

How to test

Since local dev builds use version 0.0.1 which blocks update checks, you need to temporarily fake an older version:

1. In src/Version.props, change <Version>0.0.1</Version> to <Version>0.87.0</Version>
2. Optionally, in src/runner/UpdateUtils.cpp, change both interval constants to 1 (minute) for faster testing:

   constexpr int64_t UPDATE_CHECK_INTERVAL_MINUTES = 1;
   constexpr int64_t UPDATE_CHECK_AFTER_FAILED_INTERVAL_MINUTES = 1;

3. Build and run the runner
4. Within ~1 minute (with the interval change) or after clicking 'Check for updates' in Settings > General, the runner will query GitHub and find a newer version

Verify

• Tray icon changes to the update variant (badged with orange dot)
• Right-clicking the tray icon shows 'Update available' at the top of the context menu
• Clicking 'Update available' opens Settings directly to the General page
• Settings General page shows the update InfoBar with Warning severity
• Dashboard shows the update badge with orange gradient and exclamation icon
• Quick Access flyout shows update InfoBar with Warning severity

Remember to revert Version.props and UpdateUtils.cpp before committing!