audio: make ambient music hard, fast, and aggressive

Complete rewrite of all 19 theme ambient presets to eliminate the
slow waltz/lo-fi feel.  Every preset now targets a driving rock/
industrial/hardstyle vibe with:

- **Much faster BPM**: normal 120–180, wild 180–260 (was 60–70 / 120–140)
- **Power chords** replace major/minor triads — aggressive distortion-ready
- **Straight eighth-note drive** replaces swung waltz melodies — punchy,
  rhythmic, no floaty legato
- **More active drum patterns**: double-kick, snare backbeats,
  sixteenth-note hats, clap stabs on the 16th
- **Shorter attack / release** on normal (0.3→0.02, 0.5→0.15) so everything
  hits harder
- **Higher filter cutoffs** for a brighter, more aggressive timbre
- **Three drone voices** (was 4) with lower fundamental octave, fewer
  frequencies, more focused. Sub-bass added via buildRockSong octave divider.
- **buildRockSong** replaces buildSong: adds sub-bass (/2 voice) and bass
  hits per measure, making each bar feel like a down-beat impact
- **buildDriveMelody** replaces buildSwingMelody: straight eighth notes, no swing
- **buildStabMelody** for wild mode: short 16th-note bursts with gaps

Also bumped test BPM cap from 250→400 to accommodate the new range.

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