feat(vst): S18 VST3 channel isolation — beta ReaSampler 9000 pairs with beta extension only

Fork the VST3 class UID (beta UID minted+frozen), on-disk name, and display
name by the one channel bit via app_version; couple UID selection to the
channel at compile time so a refactor can't split identity from data.

src/app_version.h

@@ -104,6 +104,33 @@ const std::string& binaryName();
 const std::string& dockTitle();
 const std::string& dockIdent();
 
+// --- VST3 instrument identity (S18, beta-in-isolation) ------------------------------
+//
+// The ReaSampler 9000 VST3 instrument forks its plugin identity per channel exactly as the
+// extension forks its binary/dock idents above — one channel per binary, all derived from
+// the ONE channel bit here, so the VST shell carries no #ifdef fork. These are the VST's
+// analogues of binaryName()/dockTitle(): the on-disk module name and the human-facing name.
+//
+//   vstOutputName() — the CMake OUTPUT_NAME base for the .vst3 module. Stable:
+//                     "reasampler_9000" (byte-identical to pre-S18). Beta:
+//                     "reasampler_9000_beta". Mirrors the CMake target's OUTPUT_NAME (the
+//                     authoritative artifact name); exposed here so the one derivation lives
+//                     in this module. FOREVER-STABLE per channel — the on-disk filename a
+//                     REAPER project's saved instance path may reference.
+//   vstPluginName() — the factory display name (FX browser), editor title band, and S6
+//                     embed-strip label. Stable: "ReaSampler 9000". Beta:
+//                     "ReaSampler 9000 beta". Sourced from here, never a literal in
+//                     reasampler_vst.h / vst_entry.cpp / the editor / the embed strip.
+//
+// NOTE: the VST3 CLASS UID is NOT here — a UID is not a string derivation but a compile-time
+// FUID/INLINE_UID constant the factory needs in brace-init form; it lives in reasampler_vst.h,
+// channel-selected by the same REASAMPLER_CHANNEL_IS_BETA bit. This module owns the string
+// identity; reasampler_vst.h owns the binary UID identity. The version display the factory
+// stamps into PClassInfo2 reuses appVersion() (it already renders "-beta" on beta) — no
+// separate VST version accessor.
+const std::string& vstOutputName();
+const std::string& vstPluginName();
+
 // --- Channel-qualified action id / name builders ------------------------------------
 //
 // The two composition helpers every action-registering shell (main.cpp, actions.cpp)