fix(vst): channel-derive the shared ext-state namespace (V4↔S4 reconcile)

ext_keys.h's kProjExtNamespace now delegates to app_version::extStateNamespace() so the beta instrument reads "reasampler_beta" — the namespace the beta extension writes — instead of stale stable. Link app_version into reasampler_vst.

CMakeLists.txt

@@ -829,8 +829,11 @@ if(WIN32)
     # give the shell TUs their headers (ext_keys.h, bank_book.h, sampler_core.h, ...).
     # embed_strip (S6): the pure inline-strip layout + hit-test the embed shell marshals
     # into; it links editor_geometry transitively (shared Rect).
+    # app_version: ext_keys.h's channel-derived namespace accessor (V4) delegates to it, so
+    # the instrument reads the SAME namespace the extension writes; its PUBLIC include dir
+    # (build/generated) carries version_generated.h for the channel bit.
     target_link_libraries(reasampler_vst PRIVATE vst3_sdk editor_geometry bridge_marshal
-        sample_map capture_paths embed_strip)
+        sample_map capture_paths embed_strip app_version)
     # SDK_INC gives reaper_vst3_interfaces.h + reaper_plugin_functions.h for the bridge;
     # WDL_INC gives LICE for the editor. The VST3 SDK headers come from vst3_sdk PUBLIC.
     target_include_directories(reasampler_vst PRIVATE ${SDK_INC} ${WDL_INC})