Sprint 1: Add AudioAnalyser.cpp stub

Source/AudioAnalyser.cpp

@@ -0,0 +1,7 @@
+#include "AudioAnalyser.h"
+
+// Phase 2: Full implementation with:
+// - prepareToPlay(sampleRate, blockSize)
+// - processBlock(buffer) — called from audio thread
+// - getCompactAnalysis() — thread-safe query from HTTP thread
+// - LUFS (Ebu128LoudnessMeter), FFT bands, stereo width, True Peak