chore: bootstrap skills library — 19 skills + installer + CI auto-tag

Phase 1 of mathias/skills extraction (infra#62 Track D — homelab
next-step plan addendum). Imports ~/dev/.skills/ verbatim (19 skill
dirs + SKILLS_INDEX.md) and adds the installation surface:

- Taskfile.yml — install / update / list / release / check targets
- install.sh — bootstrap installer for hosts without Task. Idempotent
  symlink wirer; default checkout at ~/.local/share/skills/ on every
  host; SKILLS_REF env var pins a tag (default: main).
- .gitea/workflows/release.yml — auto-tag every push to main by
  Bump-Type footer (major/minor/patch, default patch). Skipped when
  commit contains [skip-release].
- README — usage, versioning, contribution flow, secret-hygiene rule.

Phase 1 wires Claude Code only (~/.claude/skills/<name> global +
<repo>/.claude/skills/<name> per-repo). Phase 2 adds Crush, opencode,
antigravity, and gitea-resident agents (cobalt-dingo, agentsquad)
once their skill conventions are researched.

Public repo, markdown-only — no secrets, no client names. Verified
via pre-push grep before initial push.

[skip-release]

README.md

@@ -0,0 +1,81 @@
+# skills
+
+Engineering skills library — markdown `SKILL.md` files that plug into any
+project or AI-coding harness. Installed via `task skills:install` in
+consumer projects, or directly by `install.sh` on hosts without Task.
+
+## What is a skill?
+
+A skill is a single directory containing one or more markdown files. The
+canonical entrypoint is `<name>/SKILL.md`. Additional reference material
+lives alongside in the same directory (e.g.
+`clean-code/references/code-smells.md`). Harnesses load skills on
+demand — keep `SKILL.md` short and triggerable; push depth into
+references.
+
+See [`SKILLS_INDEX.md`](./SKILLS_INDEX.md) for the full catalogue with
+descriptions and "use when" triggers.
+
+## Install (consumer project)
+
+The expected pattern: each consumer project's `Taskfile.yml` has a
+`skills:install` target that delegates here. From a project root:
+
+```bash
+task skills:install
+```
+
+Bare-shell fallback for hosts without Task installed:
+
+```bash
+curl -fsSL https://gitea.d-ma.be/mathias/skills/raw/branch/main/install.sh | bash
+```
+
+Both forms are idempotent and re-runnable. On every run they:
+
+1. `git clone` (or `git pull`) this repo into `~/.local/share/skills/` —
+   the **canonical local checkout** on every host.
+2. Wire per-skill symlinks into the harnesses found on the host (see
+   [Wired harnesses](#wired-harnesses)).
+
+Re-run after `git pull` upstream to pick up new skills or version
+changes. CI tags every change as a `vX.Y.Z` release (see
+[Versioning](#versioning)).
+
+## Wired harnesses
+
+Phase 1 (current) wires **Claude Code** only:
+
+- Global: `~/.claude/skills/<name>` → `~/.local/share/skills/<name>`
+- Per-repo: `<repo>/.claude/skills/<name>` (when invoked from a git
+  repo) → same
+
+Phase 2 will add: Crush, opencode, antigravity, gitea-resident agents
+(cobalt-dingo, agentsquad). See `mathias/infra` issue `infra#62`
+addendum for the roadmap.
+
+## Versioning
+
+Every commit to `main` is auto-tagged as a semver release by the
+`.gitea/workflows/release.yml` action. Bump direction follows the commit
+footer:
+
+- `Bump-Type: major` → `X.0.0`
+- `Bump-Type: minor` → `0.Y.0`
+- *anything else* → `0.0.Z` (patch, the default)
+
+Consumer projects can pin a version by setting `SKILLS_REF=v0.1.0`
+before `task skills:install`; default is `main` for always-current.
+
+## Contributing a skill
+
+1. Add a directory `<short-kebab-name>/`.
+2. Create `<short-kebab-name>/SKILL.md` — start with one-paragraph
+   purpose, then triggers ("use when …"), then mechanics.
+3. Add a row to `SKILLS_INDEX.md` (description + use-when).
+4. Commit directly to `main`. Conventional-commit prefix
+   (`feat:` / `fix:` / `docs:`). Add `Bump-Type: minor` footer when
+   adding a new skill or expanding scope; default patch covers edits.
+
+This repo is markdown-only and public — never include secrets, client
+names, or anything under NDA in a skill.