Refine normal and wild ambient presets for all 19 themes

Replace generic ambient() helper calls with detailed ambientPreset literals
for every registered theme. Normal presets are now subtle (gain 0.02-0.03),
loopable, and low-fatigue. Wild presets are recognizably the same theme but
faster, denser, and more dramatic (gain 0.05-0.065).

Theme-specific changes:
- neon: glass drone with filter sweep; wild adds brighter arps
- terminal: CRT hum + sparse ticks; wild becomes rapid process storm
- synthwave: warm minor pad; wild doubles pulse with octave jumps
- plasma: tritone shimmer; wild adds aggressive sweep and noise
- brutalist: concrete rumble; wild adds blunt sub impacts with rhythm
- volcano: magma drone; wild adds tremor pulses and heat noise
- aurora: airy fifths; wild adds solar-storm detune shimmer
- matrix: digital rain ostinato; wild speeds code-rain pulses
- ocean: tidal swell + surf noise; wild adds storm surge
- dos: PC speaker hum; wild becomes IRQ panic at 200 BPM
- retro: amber chip tones; wild adds tape-eat jitter and noise
- cosmos: wide fifth/octave drone; wild adds supernova pulse
- retrofuture: atomic lounge pad; wild adds Geiger-like rhythm
- spaceage: theremin sines; wild adds re-entry alarm pings
- tropicale: dusk pentatonic surf; wild adds category-5 percussion
- noir: smoky minor drone; wild adds siren-like intervals
- cathedral: organ stacked sines; wild adds bell/requiem intensity
- surveillance: monitor hum/scanner; wild adds alert cascade
- biomech: organic asymmetric drone; wild adds nervous wet pulses

All generator tests pass.

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