feat(standards): MR-based tag strategy + repository inventory (registry://repos)

Versioning standard now documents the MR flow: bump pyproject.toml/VERSION and promote CHANGELOG in the MR (referencing the version/tag, not a commit id), merge/squash, then tag the resulting commit. Adds the agent-assisted tagging procedure (wait for the go-ahead, find the version-bump commit, tag only it, ask the user to push) to both the reference page and the releasing wiki runbook. Adds the repo inventory (src/repos.json -> mcp/repos.json), the registry://repos resource + list_repos tool, the 15_repository_inventory lib page, and two MCP prompts: compliance (remediate repos) and release (agent tagging).

standards/src/templates/release/CHANGELOG.md

@@ -20,16 +20,17 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Security
 
 <!--
-On release, promote the entries above into a new heading with today's date and
-leave a fresh, empty [Unreleased] section:
+In the release merge request, promote the entries above into a new heading and
+leave a fresh, empty [Unreleased] section. Name the version/tag, never a commit
+id:
 
 ## [0.1.0] - YYYY-MM-DD
 
 ### Added
 - Initial release.
 
-Then update the compare links below. See the standard:
-Versioning & Changelog (registry://release).
+Then update the compare links below. The tag is created on the merged commit —
+see the standard: Versioning & Changelog (registry://release).
 -->
 
 [Unreleased]: <repo-url>/compare/0.1.0...HEAD