feat(shortcuts): use game artwork for pinned icons

[papi-ux]

what changed

• resolve the selected Polaris games trusted square icon artwork through the existing memory, disk, and bounded fetch path
• pass that bitmap through PR #257s adaptive shortcut icon hook
• keep ic_pc_scut as the fail-closed fallback when trusted game artwork is unavailable
• preserve artwork request fencing and synchronize every memory-cache operation now used from both UI and IO threads

why

PR #257 intentionally landed the proven pinning contract first. its RP6 validation showed that Launcher3 received the generic Nova icon because the Polaris-native game-detail call hardcoded iconBits = null.

this follow-up keeps artwork separate while making the pinned home tile match the selected game.

verification

• focused RED: missing loadShortcutIcon() API
• focused GREEN: 5/5 shortcut resolver, Activity wiring, adaptive bitmap, and resource-fallback tests
• existing artwork guard suite: 18/18
• full root debug: lint passed, 1440/1440 JVM tests passed, all three debug ABIs assembled
• exact commit: 1a71e06099ef6562405e69274c1c3e825e5b54e5
• RP6 Virtual RP6_-_Virtual_-_NEW, API 37, exact x86_64 APK SHA-256 5bd358de5ce1559e3494941080a7c4b8176c5f7a4257b4dbd354c83926cfb85e
• Launcher3 accepted and pinned Phasmophobia with iconRes=0, a persisted bitmap, exact ShortcutTrampoline, host/game/HDR extras, and a visible home tile
• no game or stream was launched
• cleanup passed: shortcut removed, prior 1.3.7/39 debug APK restored byte-for-byte, pairing/library preserved, nova-lab stopped cleanly, physical Retroid untouched

boundaries

no poster cropping, second downloader, shortcut lifecycle expansion, release/tag, or physical-device mutation.