Add App Shortcuts for service control (start/stop/toggle)

[sleshep]

Add dynamic App Shortcuts for external automation

Background

The app already supports external control via intent actions (START_CLASH / STOP_CLASH / TOGGLE_CLASH) through ExternalControlActivity, and provides a Quick Settings tile via TileService. However, using these intent actions requires third-party tools like Tasker to send intents manually.

Many Android launchers and built-in automation tools (such as Samsung Routines) can natively discover and trigger App Shortcuts, but the app doesn't currently register any. Adding App Shortcuts would allow users to control the Clash service without installing additional apps.

What this PR does

Registers three dynamic App Shortcuts via ShortcutManagerCompat on app launch:

Shortcut	Action	Icon
Toggle Clash	ACTION_TOGGLE_CLASH	ic_baseline_swap_vertical_circle
Start Clash	ACTION_START_CLASH	ic_baseline_flash_on
Stop Clash	ACTION_STOP_CLASH	ic_baseline_stop

These shortcuts:

• Appear when long-pressing the app icon on any launcher
• Can be dragged to the home screen as one-tap widgets
• Are discoverable by Samsung Routines, Tasker, and other automation tools
• Support i18n (English + Chinese)

Why dynamic shortcuts (not static XML)

• shortcuts.xml requires android:targetPackage which doesn't support ${applicationId} placeholder
• The project has multiple flavors (alpha/meta) with different applicationId, dynamic shortcuts resolve the package name at runtime
• Allows future enhancement (e.g., updating shortcuts based on running state)

Changes

• app/.../MainApplication.kt — Added setupShortcuts() method called in onCreate() (main process only)
• design/.../values/strings.xml — Added 6 English shortcut label strings
• design/.../values-zh/strings.xml — Added 6 Chinese shortcut label strings

Compatibility

• Uses ShortcutManagerCompat from AndroidX (already a dependency)
• Gracefully ignored on API < 25 (Android 7.0 and below)
• No impact on existing functionality