Q-W1 code-review follow-ups: restore 104 trailing newlines, relocate reasampler_uid.h to core/wire, drop ext_keys namespaces shim, add slot_map_tests, golden serialize literals for 4 modules, namespaces.h/pragma-once ordering sweep. 60/60 green.

src/core/instrument/engine/master_gain.h

@@ -55,4 +55,4 @@ double masterGainNormFromLinear(double linear);
 // including the terminator. Pure.
 void formatMasterGainLabel(double norm, char* buf, std::size_t len);
 
-}  // namespace reasampler::instrument::engine
+}  // namespace reasampler::instrument::engine