docs(docs): add frontmatter to asset pipeline docs

Standardized YAML frontmatter on all 13 docs/assets/ files covering
audio, visual, and video pipeline docs, palettes, and templates.

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

docs/assets/audio/README.md

@@ -1,3 +1,10 @@
+---
+title: "Audio Asset Pipeline"
+description: "Audio pipeline index with category status, generation tools, bus architecture, and sprint scope"
+type: design
+status: active
+---
+
 # Audio Asset Pipeline
 
 Status: **Active** — Sprint 7 (first audio sprint)

docs/assets/audio/ambient.md

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+---
+title: "Ambient Audio Assets"
+description: "Zone-based ambient loop assets for station base and zone overlays with generation and layering specs"
+type: design
+status: active
+---
+
 # Ambient — Audio Assets
 
 Zone-based ambient loops. Station base plays globally; overlays crossfade based on player zone (hard tile boundary, 1.5-2s audio tween).

docs/assets/audio/palette.md

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+---
+title: "Audio Palette"
+description: "Sonic identity guide covering insert-tech and organic families, station palette, bus architecture, and generation approach"
+type: design
+status: active
+---
+
 # Audio Palette
 
 The sonic identity of The Settled Reach. Living document — updated as the audio language evolves.

docs/assets/audio/sfx.md

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+---
+title: "SFX Audio Assets"
+description: "World sound effect assets for footsteps, NPC murmur, and environmental events with generation specs"
+type: design
+status: active
+---
+
 # SFX — Audio Assets
 
 World sound effects: footsteps, environmental events, impacts. Event-driven, often positional (AudioStreamPlayer2D).

docs/assets/audio/ui.md

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+---
+title: "UI Audio Assets"
+description: "Interface sound assets for cursor, implant, monologue chimes, and weapon aim with generation specs"
+type: design
+status: active
+---
+
 # UI — Audio Assets
 
 Interface sounds triggered by player interaction, insert systems, and cognitive events. Non-positional (AudioStreamPlayer). Routes to UI Sounds bus.