feat(bluecraft-agentic-docs): add agentic docs skill templates

Add the Bluecraft Agentic Docs skill with guidance for maintaining
root `AGENTS.md` files and `agent-docs/` trees.

Include OpenAI agent metadata plus reference templates and checklists
for root routing, rule docs, inventory docs, and refactor validation.

skills/bluecraft-agentic-docs/references/rule-doc-template.md

@@ -0,0 +1,35 @@
+# Rule `agent-docs/` Template
+
+Use this structure for Markdown files inside `agent-docs/` when the document's main job is to govern behavior: rules, policy, constraints, decision criteria, or workflow guidance.
+
+## Recommended Shape
+
+```md
+# <Document Title>
+
+<Opening statement: what this doc governs, when it applies, and that it must be followed in scope.>
+
+## Applies To
+
+- <specific task or document types>
+
+## Does Not Apply To
+
+- <out-of-scope task or document types>
+
+## <Rule Section>
+
+- <instructions>
+
+## Checklist
+
+- <validation questions>
+```
+
+## Notes
+
+- Make the scope explicit.
+- Keep the document responsible for one topic.
+- Use semantic filenames and headings.
+- State the user or maintainer decision directly: what to do, what to avoid, and how to choose.
+- Prefer linking to inventories, examples, or narrower child docs instead of embedding long registries inline.