feat: implement Phase 10.1 & 10.2 - frequency analyzer and spectrogram

Added real-time audio analysis visualizations to master column:

- FrequencyAnalyzer component with FFT bar display
  - Canvas-based rendering with requestAnimationFrame
  - Color gradient from cyan to green based on frequency
  - Frequency axis labels (20Hz, 1kHz, 20kHz)

- Spectrogram component with time-frequency waterfall display
  - Scrolling visualization with ImageData pixel manipulation
  - Color mapping: black → blue → cyan → green → yellow → red
  - Vertical frequency axis with labels

- Master column redesign
  - Fixed width layout (280px)
  - Toggle buttons to switch between FFT and Spectrum views
  - Integrated above master controls with 300px minimum height

- Exposed masterAnalyser from useMultiTrackPlayer hook
  - Analyser node now accessible to visualization components

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

lib/hooks/useMultiTrackPlayer.ts

@@ -830,6 +830,7 @@ export function useMultiTrackPlayer(
     masterPeakLevel,
     masterRmsLevel,
     masterIsClipping,
+    masterAnalyser: masterAnalyserRef.current,
     resetClipIndicator,
     play,
     pause,