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/root-agents-template.md

@@ -0,0 +1,29 @@
+# Root `AGENTS.md` Template
+
+Use this structure for the `AGENTS.md` at the root of the current Git working tree.
+
+## Recommended Shape
+
+```md
+# Root Entry
+
+- State that this file is the primary routing entrypoint for the repository's agentic documentation tree.
+- Define the default path basis.
+
+# Common Constraints
+
+- Keep repository-wide rules here.
+- Do not repeat topic-specific rules that belong in child docs.
+
+# Required Instructions Before Editing
+
+- Route to the required child instruction docs.
+- Use explicit "Read and follow ..." wording.
+```
+
+## Notes
+
+- Keep this file short.
+- Treat this file as an instruction document, not a passive index.
+- Route to child docs only when they are actually needed.
+- Do not turn the root file into a dump of all topic-specific rules.