[Epic Sub-task] Cheat Code Export, QR Sharing & App Group Sync (Paid IAP)

[github-actions]

Cheat Code Export, QR Sharing & App Group Sync (Paid IAP)

Extend the existing cheat code system (local SQLite DB + online lookup already merged) with export, QR code sharing, and cross-app synchronisation via App Groups.

Value Proposition

• Users can export any cheat to the clipboard in the correct format for their target emulator
• QR codes let users scan cheat codes directly onto a retro console (via a phone or printed card)
• App Group container (group.org.provenance-emu.provenance) shares a curated cheat library between the main app, companion app, and extensions — no cloud required
• Paid feature via StoreKit 2 IAP: org.provenance-emu.companion.iap.cheat-library

Implementation Plan

PVLibrary additions

• SharedCheatStore actor — reads/writes a shared-cheats.json file in the App Group container; exposes add(_:), remove(id:), loadAll() — allows any app in the group to share favourited cheat codes

PVUI additions

• CheatQRCodeGenerator — CoreImage/CIFilter pipeline to generate a UIImage QR code from a compact provenance-cheat:// URL encoding (name + code + format + system)
• CheatExportView — SwiftUI sheet showing: large QR code, raw code text, Copy button, ShareLink; guards premium tiers behind the IAP entitlement check

Companion App / DriverProduct

• New IAP product: cheatLibrary — org.provenance-emu.companion.iap.cheat-library
• Expose a "Cheats" tab or section in the companion app's Library tab

Part of #3201