feat: add docs checker and record templates

docs new creates ADRs and plans from embedded templates; docs check reports
path:line: message problems per docs/docs-format.md.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/docs/templates/plan.md

@@ -0,0 +1,20 @@
+---
+status: draft
+tracking: []
+adrs: []
+completion: []
+---
+
+# @TITLE@
+
+## Scope
+
+{{docs:todo}}
+
+## Steps
+
+{{docs:todo}}
+
+## Validation
+
+{{docs:todo}}