Add unique ambient melodies for all 19 themes

Each theme now has a distinctive looping melodic phrase (normal + wild variants)
played by the Web Audio ambient engine. This replaces the generic random-pulse
behavior that made all themes sound the same.

Go changes:
- Add melodyNote struct with freq/dur/gain fields to ambientPreset
- Add n() helper for concise melody construction
- Rewrite all 19 theme presets with unique melodic phrases:
  neon=glassy arpeggio, terminal=sparse CRT beeps, synthwave=warm minor,
  plasma=tritone shimmer, brutalist=concrete rumble, volcano=phrygian,
  aurora=high shimmer, matrix=digital ostinato, ocean=wave flow,
  dos=8-bit arpeggio, retro=VHS warmth, cosmos=vast fifths,
  retrofuture=lounge minor-7, spaceage=pure ascending, tropicale=pentatonic,
  noir=smoky minor-7, cathedral=organ thirds, surveillance=fourth alert,
  biomech=diminished unease

JS changes:
- Add melodyTimer/melodyIndex state to ambient engine
- Add playMelodyNote() with per-note gain and filter support
- Add scheduleMelodyNote() with phrase-rest gaps
- schedulePulse() now routes to melody player when melody is present
- Add sawtooth support to snonuxWaveType()
- Reset melody index on startEngine() and stopAll()

Test changes:
- TestThemeSoundPresetsAmbientPopulated now accepts melody as valid content
- TestThemeSoundPresetsAmbientValuesBounded validates melody note freq/dur

0 files changed, 0 insertions, 0 deletions