Add support for launching pinned shortcuts (PWAs)

[watchdogeditor]

Browsers pin a shortcut (via ShortcutManager.requestPinShortcut) when you "Add to Home screen" for a site they can't package as a WebAPK -- self-hosted pages, Firefox, or devices without Play Services. HomeActivity already declared the CONFIRM_PIN_SHORTCUT intent filter, but nothing handled the request, so the pinned shortcut was silently dropped.

Handle it and treat a pinned shortcut as a first-class launcher item:

• Represent it as an AppIcon with a synthetic ComponentName plus shortcutPackage/shortcutId, so it flows through the existing app map, drawer, search, pie menu and menu persistence unchanged.
• Launch via LauncherApps.startShortcut() from the single dispatch point in AppLauncher.launchApp().
• Persist in a new pinned_shortcuts table (db version 4) and re-inject on every index so shortcuts survive reindexing and reboots.
• Accept the request in HomeActivity (onCreate and onNewIntent), auto-adding with a toast.
• Remove a shortcut by dragging it onto the pie editor's uninstall target (ending edit mode cleanly); "Show app info" opens the owning app instead.