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/test-plan.md

@@ -0,0 +1,28 @@
+---
+title: ""                    # Display name (e.g., "Fog Rendering Visual Test Plan")
+description: ""              # One-line summary for context filtering (e.g., "Test coverage for fog shader: gradient smoothness, alpha tuning, performance budgets")
+type: test-plan              # architecture | design | briefing | workshop | test-plan | test-report | audit
+status: active               # active | draft | archived | superseded
+ticket: ""                   # Ticket reference
+system_under_test: ""        # What system/feature is being tested
+created: YYYY-MM-DD
+updated: YYYY-MM-DD
+---
+
+# {Title}
+
+## Scope
+
+{What is being tested and what is excluded.}
+
+---
+
+## Test Cases
+
+{Numbered test cases with expected results.}
+
+---
+
+## Environment
+
+{Test environment requirements: live server, fixtures, headless, etc.}