Add doubynet skill and extend check_versions.py to cover installed skills

CHANGELOG.md

@@ -7,6 +7,32 @@ ships documents, so it uses the same `v#` scheme as the documents themselves.
 Individual guideline documents carry their own `Document Version` header, and the skills carry
 `metadata.version`; both are independent of the revisions below.
 
+## v9 — 2026-10-07
+
+### Added
+- `Claude/skills/doubynet/` — new personal skill, reconciles the DoubyNet home-network
+  documentation (a separate Syncthing-synced tree, not part of this repository) against
+  the live state of its hosts, reports discrepancies, and updates the affected `.md`
+  files. Versioned `v1`, following the established `metadata.version` convention. Was
+  already in use directly from `~/.claude/skills/doubynet/` without a master copy here;
+  brought in after a session surfaced several gaps (stale hardcoded path, unclear
+  historical-vs-live document handling, no mention of CHANGELOG.md, no guidance for
+  facts that can't be verified from a machine at all) that were fixed in the same pass
+- `check_versions.py` now also checks the master skills in `Claude/skills/<name>/SKILL.md`
+  against their installed copies in `~/.claude/skills/<name>/SKILL.md` — a fixed location,
+  independent of `--root`. Reads `metadata.version` from the YAML frontmatter instead of
+  the `**Document Version:**` marker used by guideline documents. A skill missing from
+  `~/.claude/skills/` entirely is reported as a new status, `MISSING`, and is safe to
+  `--sync` like `BEHIND`. Prompted by running the tool for the first time since `doubynet`
+  was added: it found four of the five pre-existing skills installed without any version
+  header at all, and `documentation_context` missing from `~/.claude/skills/` entirely
+
+### Changed
+- `--sync`/report wording generalised from "document(s)" to "item(s)" now that the same
+  machinery covers both guideline documents and skills
+
+---
+
 ## v8 — 2026-09-29
 
 ### Fixed