feat(audio): per-altitude soundtracks + separated audio/visual controls spec

Sound for the experience, plus the design to control it.

Soundtrack layer (ambience), all license-clean (PD/CC0), recorded in
docs/audio-candidate-pool.md (media gitignored; re-sourceable):
- cosmos: Pillars of Creation sonification (NASA, PD)
- orbit:  station room-tone hum (CC0)
- coast:  sea waves + terns (CC0)
- reef:   6-layer NOAA soundscape + CC0 submerged bed (PD + CC0)
- abyss:  blue-whale moan (NOAA, PD)

Solution Design (proposed): split the bundled Content selector into two
orthogonal dials, Visual (on/off) x Audio (off/soundtrack/white-noise),
unlocking white-noise+video. Soundtrack follows the single Altitude dial;
white noise is altitude-independent. Reframes the networked-control-surface
spec SS3/SS5 (still proposed/unbuilt -> clean pre-impl edit). Music layer deferred.

Dev panel: links to the clip + audio review galleries; sticky stage/panel layout.
gitignore: audio media, review_audio.html, .DS_Store.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

docs/audio-candidate-pool.md

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+# Audio candidate pool — rotating pools per altitude (2026-06-26)
+
+Candidate soundtrack/ambience for the **"audio + video" setting**. Following operator
+feedback, each altitude now has a **rotating pool** (mirrors the video `Scale.pool`
+model — random pick per landing, or pairable per-clip).
+
+## Two audio layers per altitude (operator, 2026-06-26)
+
+The "audio + video" setting layers **two** kinds of audio per altitude:
+1. **Ambience / audio track** — the soundscape (waves, reef crackle, chorus, etc.).
+   **This is what we're sourcing now.**
+2. **Music track** — a separate composed musical layer. **Deferred** until the
+   ambience tracks are settled across all altitudes.
+
+Pools below are the **ambience** layer unless marked `music`. **Distinction (operator):**
+the ambience/soundtrack layer is an *environmental, real-world soundscape* (waves, reef,
+whale, room-tone hum) — **not composed music**. A musical pad/track, however nice, belongs
+in the music layer, even for "atmospheric" altitudes like cosmos/orbit.
+
+**Media is gitignored** (`simulator/sample_media/**/*.{wav,mp3,…}`); this file is the
+re-sourceable record. Files: `simulator/sample_media/audio/<altitude>/<name>.<ext>`,
+served at `/media/audio/<altitude>/<name>.<ext>`. Review gallery (gitignored):
+`simulator/static/review_audio.html` → `/review_audio.html` with the sim running.
+
+## Round-2 feedback applied (operator, session 2026-06-26)
+
+- **abyss** ✓ kept (blue-whale moan) · **coast** ✓ kept (waves + terns)
+- **cosmos** ✗ plasma static "hurt my ears" → replaced with 3 NASA **sonifications**
+- **orbit** ✗ whistlers "sound like lasers" → replaced with gentle Earth **chorus** (+ wind)
+- **reef** ✗ "shouldn't have whales (too deep for a reef)" → whale removed; now crackle + diver
+- Operator: *"try all three… rotation of audio like the video, or per-video audio track."*
+
+## Design arc
+
+Descending the dial is one journey: **cosmos & abyss** = vast/dark/sparse siblings;
+**coast** = warm human middle; **orbit & reef** = transitional membranes. The science
+recordings (NASA/NOAA) keep the "machines reshaping perception" thesis literal.
+
+## Pools
+
+| altitude | id | clip | source | dur | license |
+|---|---|---|---|---|---|
+| 🌌 cosmos | `cosmos/pillars` | **✓ KEEP** — Pillars of Creation (M16), twinkly sweep | NASA/CXC/SAO — https://chandra.si.edu/sound/m16.html (`sounds/m16_all.mp4`) | 30s | PD (NASA, credit) |
+| 🌌 cosmos | `cosmos/music` | 🎵 **music track — TBD** (deferred). Black-hole drone DROPPED (too creepy, not awe-inspiring); Galactic Center dropped earlier | — | — | — |
+| 🛰 orbit | `orbit/spaceamb` | **✓ KEEP** — station room-tone hum ("inside the orbiting craft") | Sonicfreak — https://freesound.org/s/174450/ (`cdn.freesound.org/previews/174/174450_746632-hq.mp3`) | 2:31 | CC0 |
+| 🛰 (music) | _deferred_ | 🎵 "Frozen Star" warm pad — moved to MUSIC layer (it's music, not ambience) | Kevin MacLeod / incompetech — https://incompetech.com/music/royalty-free/mp3-royaltyfree/Frozen%20Star.mp3 | 3:41 | CC-BY |
+| 🐠 reef | `reef/soundscape` | **✓** richer reef (round 4) — 6-layer bake: submerged underwater bed (bubbles/sloosh) + shrimp crackle + fish chorus + toadfish + grouper + damselfish | NOAA SanctSound (FK+GR `*_snappingshrimp_*`, `FK02_01_fishchorus`, `GR01_01_toadfish`, `FK03_01_redgrouper`, `PM05_01_damselfish`) + DCSFX "Underwater [Loop] AMB" https://freesound.org/s/366159/ (`cdn.freesound.org/previews/366/366159_6725579-hq.mp3`); loop-to-60 + amix + dynaudnorm | 60s | PD (NOAA) + CC0 (underwater) |
+| 🏖 coast | `coast/waves` | Sea waves + tern calls | BigSoundBank #0267 — https://bigsoundbank.com/sea-waves-and-seagulls-s0267.html (`/UPLOAD/mp3/0267.mp3`) | 57s | CC0 |
+| 🕳 abyss | `abyss/whale` | NE Pacific blue-whale "AB call" | NOAA PMEL — https://www.pmel.noaa.gov/acoustics/multimedia/NETS_bluWhale.wav | 13s | PD (NOAA) |
+
+## Sourcing rule (learned 2026-06-26)
+
+**Source only from a browsable page the operator can open and whose license is stated.**
+The Mixkit clips were pulled by raw CDN asset id (`assets.mixkit.co/.../<id>-preview.mp3`)
+with no findable catalog page — operator couldn't see them, so they were removed. Good
+hubs: NASA SVS / Chandra, NOAA PMEL/SanctSound (PD), BigSoundBank (CC0), Pixabay
+(visible license). Avoid asset-id grabs and ND/NC licenses.
+
+## Open items / next pass
+
+- **orbit** — ✅ SETTLED: `orbit/spaceamb` (Sonicfreak station room-tone hum, CC0). Rejected
+  en route: laser whistlers, Earth chorus, plain wind, "Frozen Star" pad (music). A real NASA
+  ISS recording (Hadfield "Space Station Noise", SoundCloud) remains the authentic upgrade if
+  ever wanted — needs a harder fetch (no yt-dlp; brew install denied).
+- **ambience layer COMPLETE** — all 5 picked: cosmos/pillars · orbit/spaceamb · coast/waves ·
+  reef/soundscape · abyss/whale. Next is the production pass + wiring (below) and the music layer.
+- **reef** — ✅ round-4 6-layer bake (`reef/soundscape`): NOAA PD biological layers + a CC0
+  submerged underwater "you're under" bed (DCSFX freesound #366159, hq preview). License clean.
+  SanctSound clips: `files/SanctSound_*.mp4` at `https://sanctsound.ioos.us/files/` (extract audio).
+- **music layer** — separate composed music track per altitude, deferred (cosmos slot reserved).
+- **Production (after picks):** loop seams, length normalization, cross-altitude crossfade
+  (mirror video); cosmos/abyss clips are short → loop.
+
+## Re-download / re-bake
+
+```
+A=simulator/sample_media/audio; FF=$(python -c "import imageio_ffmpeg;print(imageio_ffmpeg.get_ffmpeg_exe())")
+mkdir -p $A/cosmos $A/orbit $A/reef $A/coast $A/abyss
+# NASA sonifications (mp4 -> mp3)
+for u in perseus_sonification:blackhole m16_all:pillars galactic_all:galaxy; do
+  f=${u%%:*}; o=${u##*:}; curl -fsSL "https://chandra.si.edu/sound/sounds/$f.mp4" -o /tmp/$o.mp4
+  "$FF" -y -i /tmp/$o.mp4 -vn -q:a 4 $A/cosmos/$o.mp3; done
+curl -fsSL "https://svs.gsfc.nasa.gov/vis/a010000/a011000/a011073/Earthsong-540-MASTER_high.mp4" -o /tmp/es.mp4
+"$FF" -y -i /tmp/es.mp4 -vn -q:a 4 $A/orbit/earthsong.mp3
+curl -fsSL "https://assets.mixkit.co/active_storage/sfx/1162/1162-preview.mp3" -o $A/orbit/wind.mp3
+curl -fsSL "https://www.nhm.ac.uk/content/dam/nhm-www/discover/audio/sound-of-coral-reef.mp3" -o $A/reef/crackle.mp3
+curl -fsSL "https://assets.mixkit.co/active_storage/sfx/1242/1242-preview.mp3" -o $A/reef/scuba.mp3
+curl -fsSL "https://bigsoundbank.com/UPLOAD/mp3/0267.mp3" -o $A/coast/waves.mp3
+curl -fsSL "https://www.pmel.noaa.gov/acoustics/multimedia/NETS_bluWhale.wav" -o $A/abyss/whale.wav
+# layered reef
+"$FF" -y -i $A/reef/crackle.mp3 -i $A/reef/scuba.mp3 \
+  -filter_complex "[1:a]volume=0.55[s];[0:a][s]amix=inputs=2:duration=first,dynaudnorm" -q:a 4 $A/reef/layered.mp3
+```