docs(assets): add asset pipeline documentation system

Category-based asset index for audio, visual, and video pipelines.
Audio pipeline fully populated: palette (sonic identity bible), ambient
loops, SFX, UI sounds with generation specs and mix parameters.
Visual and video are stubs pending their respective workshops.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/assets/visual/README.md

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+# Visual Asset Pipeline
+
+Status: **Stub** — awaiting first visual sprint.
+
+## Categories
+
+| Category | File | Count | Description |
+|----------|------|-------|-------------|
+| Sprites | [sprites.md](sprites.md) | 0 | Entity sprites via 3D render pipeline |
+| Furniture | [furniture.md](furniture.md) | 0 | Furniture items by location/type |
+| Tilesets | [tilesets.md](tilesets.md) | 0 | Floor/wall tiles by biome/planet |
+| Icons | [icons.md](icons.md) | 0 | UI icons, status indicators |
+| Effects | [effects.md](effects.md) | 0 | Fog shaders, particles, overlays |
+
+## Palette
+
+See [palette.md](palette.md) for art direction, "the angle", color relationships, and render pipeline specs.
+
+## Pipeline
+
+- **3D render pipeline:** Blender model → Godot Camera3D at -72.5deg → orthographic render → outline pass → resolution downscale
+- **Render skill:** `/render-sprite` produces 12 PNGs (4 directions x 3 resolutions)
+- **Art direction workshop:** `docs/workshops/art-direction-mood-board/`
+
+## Decision References
+
+- D-019: Top-down camera, 15-20deg from vertical ("the angle")
+- D-033: Entity color = relationship to player
+- D-045: Environmental neutrality

docs/assets/visual/palette.md

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+# Visual Palette
+
+Status: **Stub** — reference art direction workshop output for current guidance.
+
+See `docs/workshops/art-direction-mood-board/` for the established visual identity.
+
+## Key Decisions
+
+- **Camera angle:** 15-20deg from vertical ("the angle"), rendered via orthographic Camera3D at -72.5deg from horizontal (D-019)
+- **Entity colors:** Relationship-based per D-033 (green = known/friendly, amber = neutral, red = hostile, etc.)
+- **Environmental neutrality:** Spaces don't visually shift with narrative state (D-045)
+- **Functional warmth:** Industrial infrastructure that people made livable — not military, not luxury
+
+## Style Guide
+
+To be populated from art direction workshop synthesis and first visual sprint.