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/_templates/audio.md

@@ -1,3 +1,10 @@
+---
+title: "Audio Asset Template"
+description: "Row and detailed entry templates for audio asset documentation"
+type: design
+status: active
+---
+
 # Audio Asset Template
 
 ## Table Row Format

docs/assets/_templates/sprite.md

@@ -1,3 +1,10 @@
+---
+title: "Sprite Asset Template"
+description: "Row and detailed entry templates for sprite and visual asset documentation"
+type: design
+status: active
+---
+
 # Sprite Asset Template
 
 ## Table Row Format

docs/assets/_templates/video.md

@@ -1,3 +1,10 @@
+---
+title: "Video Asset Template"
+description: "Row and detailed entry templates for video asset documentation"
+type: design
+status: active
+---
+
 # Video Asset Template
 
 ## Table Row Format