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.cpp

@@ -86,6 +86,24 @@ const std::string& dockIdent() {
     return kIdent;
 }
 
+const std::string& vstOutputName() {
+    // The .vst3 module OUTPUT_NAME base — FOREVER-STABLE per channel. Stable is
+    // byte-identical to pre-S18 ("reasampler_9000"); beta is isolated so both install
+    // side-by-side without a filename collision.
+    static const std::string kName =
+        kIsBeta ? "reasampler_9000_beta" : "reasampler_9000";
+    return kName;
+}
+
+const std::string& vstPluginName() {
+    // The factory display name / editor title / embed label. Stable is byte-identical to
+    // pre-S18 ("ReaSampler 9000"); beta appends " beta" so the two channels are distinct
+    // plugins in the FX browser.
+    static const std::string kName =
+        kIsBeta ? "ReaSampler 9000 beta" : "ReaSampler 9000";
+    return kName;
+}
+
 std::string channelCommandId(const std::string& suffix) {
     return commandIdPrefix() + suffix;
 }