fix(processor): close S-VIEW-4 previewVelocity persistence loop

Add previewVelocity_ member to ReaSamplerProcessor; populate it in
getState and restore it in setState so the field round-trips in the
plugin, not just in the pure unit test. Clamp 1..127 at the
deserialize read boundary in sample_map.cpp.

src/vst/sample_map.cpp

@@ -628,7 +628,11 @@ ComponentState deserializeComponentState(const std::vector<std::uint8_t>& bytes,
     if (!r.ok) return out;  // truncated before/inside the marker -> empty (marker 0 holds)
     const std::uint8_t previewVel = r.u8();
     if (!r.ok) return out;  // truncated before the velocity byte -> empty (mid default holds)
-    out.previewVelocity = previewVel;
+    // Clamp to the documented MIDI 1..127 range: a 0 byte (or any out-of-spec value from a
+    // corrupt blob) falls back to the mid default rather than silencing the preview trigger.
+    out.previewVelocity = (previewVel >= 1 && previewVel <= 127)
+                              ? previewVel
+                              : kPreviewVelocityDefault;
     const std::uint32_t idLen = r.u32();
     out.selectionId = r.str(idLen);
     if (!r.ok) { out.selectionId.clear(); return out; }  // truncated id -> empty