docs(docs): add frontmatter templates for docs/ directory

New template system for project documentation with standardized
frontmatter (title, description, type, status, decision_refs).
Templates for architecture, design, briefing, workshop, and test-plan
document types. Enables context-aware loading alongside the existing
wiki template system.

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

docs/_templates/design.md

@@ -0,0 +1,35 @@
+---
+title: ""                    # Display name (e.g., "Monologue Content Architecture")
+description: ""              # One-line summary for context filtering (e.g., "Authoring contract for internal monologue: categories, triggers, volume targets")
+type: design                 # architecture | design | briefing | workshop | test-plan | test-report | audit
+status: active               # active | draft | archived | superseded
+ticket: ""                   # Ticket reference (e.g., "#253")
+decision_refs: []            # e.g., [D-016, D-032]
+author: ""                   # Primary author agent or person
+created: YYYY-MM-DD
+updated: YYYY-MM-DD
+---
+
+# {Title}
+
+## Purpose
+
+{What this document defines and who should use it.}
+
+---
+
+## Specification
+
+{The design itself: rules, formats, examples, constraints.}
+
+---
+
+## Examples
+
+{Concrete examples showing correct usage.}
+
+---
+
+## Decision References
+
+{Link to relevant D-records and explain how they constrain this design.}