chore(agents): install mattpocock skills + per-repo agent config

- 38 skills from mattpocock/skills into .agents/skills/ (symlinked into
  .claude/skills/ for Claude Code)
- skills-lock.json for reproducible installs
- docs/agents/: issue-tracker (Gitea via tea CLI), triage-labels
  (default five-role vocabulary), domain docs (single-context)
- CLAUDE.md: add '## Agent skills' section pointing at docs/agents/
- .gitignore: un-ignore docs/agents/ under the local /docs/* rule

CLAUDE.md

@@ -878,3 +878,17 @@ side if exposing beyond a trusted network.
   package manager: `apt install libimage-exiftool-perl`,
   `brew install exiftool`, `winget install OliverBetz.ExifTool`, or
   `choco install exiftool`.
+
+## Agent skills
+
+### Issue tracker
+
+Issues live on Gitea (`git.crkc.xyz/Apps/ImageApi`); use the `tea` CLI for all operations. See `docs/agents/issue-tracker.md`.
+
+### Triage labels
+
+Default vocabulary: `needs-triage`, `needs-info`, `ready-for-agent`, `ready-for-human`, `wontfix` (label string = role name). See `docs/agents/triage-labels.md`.
+
+### Domain docs
+
+Single-context: one `CONTEXT.md` + `docs/adr/` at the repo root. See `docs/agents/domain.md`.