docs(docs): add frontmatter to all design docs

Standardized YAML frontmatter on all 40 docs/design/ files with title,
description, type, status, ticket, decision_refs, and author fields.
Covers specs, wireframes, voice cards, spatial layouts, and system
designs.

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

docs/design/knowledge-flags-v01.md

@@ -1,3 +1,15 @@
+---
+title: "Knowledge Flags — v0.1 Quick Reference"
+description: "Quick reference of valid fact IDs, prerequisite formats, and starting knowledge for monologue content authoring"
+type: design
+status: active
+ticket: "#309"
+decision_refs: [D-028, D-035, D-041, D-075]
+author: ""
+created: 2026-02-19
+updated: 2026-02-19
+---
+
 # Knowledge Flags — v0.1 Quick Reference
 
 **For:** Mellanie (content authoring), Paula (narrative design)