fix: thin libretro wrapper hijacking RA cores when feature flag is off

PVCoreFactory probed `NSClassFromString("PVRetroArchCore")` to decide whether
the legacy RA wrapper was available, but the actual Swift class is exposed to
the ObjC runtime as `PVRetroArch.PVRetroArchCoreCore` (module-prefixed). The
probe always returned nil, so `!pvRetroArchCoreExists` was always true and the
thin wrapper swap fired unconditionally — even with the feature flag disabled.

Probe the principleClass we were actually asked to load instead. If it resolves
the legacy wrapper is in this build, and we only swap when the feature flag
explicitly opts in.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Author: JoeMatt

PVUI/Sources/PVUIBase/Emulator/PVCoreFactory.swift

@@ -34,8 +34,13 @@ public extension PVCore {
         ILOG("createInstance: principleClass=\(className) for \(identifier)")
         if className.contains("RetroArch") || className.contains("LibRetro") || className == "PVRetroArchCoreBridge" {
             let featureEnabled = PVFeatureFlags.shared.isEnabled(.dynamicLibretroScanner)
-            let pvRetroArchCoreExists: Bool = NSClassFromString("PVRetroArchCore") != nil
-            ILOG("ThinLibretro: featureEnabled=\(featureEnabled)")
+            // The Swift class is exposed to the ObjC runtime as `PVRetroArch.PVRetroArchCoreCore`
+            // (module-prefixed), so the previous `NSClassFromString("PVRetroArchCore")` always
+            // returned nil and unconditionally forced the thin wrapper. Probe the actual
+            // principleClass we were asked to load instead — if it resolves, the legacy wrapper
+            // is available and we should only swap when the feature flag explicitly says so.
+            let pvRetroArchCoreExists = NSClassFromString(className) != nil
+            ILOG("ThinLibretro: featureEnabled=\(featureEnabled), legacyClassExists=\(pvRetroArchCoreExists) (probed=\(className))")
             if featureEnabled || !pvRetroArchCoreExists {
                 // Force-load PVCoreBridgeRetro framework so the ObjC runtime has
                 // PVThinLibretroCore registered. Frameworks are lazily loaded and