feat: image-baked agent skills + pi-devbox-environment skill (v1.2.0)

Ship skills inside the image (independent of any mounted skillset repo):
- rootfs/usr/local/share/pi-devbox/skills/<name>/ symlinked into
  ~/.agents/skills/ by entrypoint-user.sh (foreign-link, survives volume
  recreate, never clobbers a skillset/user skill of the same name).
- New pi-devbox-environment skill: persistence model, host/LAN SSH
  reachability, split-DNS mechanisms, interactive-vs-tool-shell alias
  gotcha, tmux 0-index, uv-first Python, pi-studio reachability. Agnostic
  to host OS / hostnames / domains / nameservers (discovered at runtime).
- Dockerfile.variant appends pi-global-AGENTS.append.md onto pi-toolkit's
  pi-global-AGENTS.md (single global slot) so the skill is loaded
  proactively; gated on /usr/local/lib/pi-devbox/. Idempotent.
- smoke-test: baked-skill + append-snippet + merged-marker presence and a
  runtime symlink assertion.
- docs: README 'Agent skills' section, AGENTS.md layout, DOCKER_HUB.md;
  moved studio-tex roadmap to v1.3.0.

pi 0.79.7 -> 0.79.10 (auto-resolved from npm latest at build).

CHANGELOG.md

@@ -11,6 +11,52 @@ Pre-v1.0.0 tags followed the pi npm version (`v{pi_version}[letter]`).
 
 ---
 
+## v1.2.0 — 2026-06-22
+
+Minor release: **image-baked agent skills** — a new base mechanism that ships
+skills inside the image (independent of any mounted skillset repo) — plus the
+first such skill, `pi-devbox-environment`, and pi `0.79.9` → `0.79.10`
+(auto-resolved from npm `latest` at build).
+
+### Added
+
+- **Image-baked agent skills.** Skills under
+  `/usr/local/share/pi-devbox/skills/<name>/` are now symlinked into
+  `~/.agents/skills/` by `entrypoint-user.sh` on every start, making them
+  available **with or without** a mounted `skillset` repo. The symlink points
+  at the image path (so it survives volume recreate, unlike anything baked
+  under a home dir a named volume would shadow) and is created only when
+  absent, so a same-named skillset skill or user override is never clobbered.
+  The skillset deploy classifies these as foreign-links and its `--prune-stale`
+  pass leaves them untouched.
+- **`pi-devbox-environment` skill** (the first image-baked skill). Teaches
+  agents the container-shaped facts that are easy to get wrong: the
+  persistence/ephemerality tier model (what survives `down -v` / image
+  update), host + LAN SSH reachability and ControlMaster, split-horizon DNS
+  *mechanisms*, the interactive-vs-tool-shell alias gotcha (`dssh`/`dscp`/
+  `cat`→`bat` don't exist in the non-interactive bash tool), the tmux 0-index
+  constraint, uv-first Python, and pi-studio reachability. Deliberately
+  environment-agnostic — host OS, hostnames, internal domains, and nameservers
+  are discovered at runtime, never hardcoded.
+- **Proactive skill awareness via the global `AGENTS.md`.** `Dockerfile.variant`
+  appends a short, gated pointer (`pi-global-AGENTS.append.md`) onto
+  pi-toolkit's `pi-global-AGENTS.md` — the single global instruction slot pi
+  loads at startup — so containers load the `pi-devbox-environment` skill
+  proactively rather than only on description match. The pointer fires only
+  inside a pi-devbox container (checks for `/usr/local/lib/pi-devbox/`).
+  Build-time append is idempotent via a marker grep; runtime is unaffected
+  (the file is root-owned and re-symlinked by pi-toolkit each boot).
+- **Smoke-test coverage** for the new mechanism: build-time presence of the
+  baked skill + append snippet + the merged marker in `pi-global-AGENTS.md`,
+  and a runtime assertion that `~/.agents/skills/pi-devbox-environment` is
+  linked after the entrypoint runs.
+
+### Bumped: pi 0.79.9 → 0.79.10
+
+Resolved from npm `latest` at build (v1.1.7 shipped `0.79.9`). See the
+[pi changelog](https://github.com/earendil-works/pi/blob/main/CHANGELOG.md)
+for the upstream `0.79.10` notes.
+
 ## v1.1.7 — 2026-06-21
 
 Patch release: pi `0.79.8` → `0.79.9` (auto-resolved at build), plus the
@@ -111,8 +157,6 @@ Notable upstream changes (from [pi releases](https://github.com/earendil-works/p
   reproducibility. Resolution now validates each result is a 40-hex commit
   SHA (and pi a real semver) and aborts the release otherwise.
 
----
-
 ## v1.1.5 — 2026-06-18
 
 Patch release: SSH ControlMaster read-only-socket fix + pi `0.79.6` → `0.79.7`
@@ -507,7 +551,7 @@ dependencies.
 ### Future work
 
 - v1.1.0: `:latest-studio` variant (adds [pi-studio](https://github.com/omaclaren/pi-studio)).
-- v1.2.0: `:latest-studio-tex` variant (adds texlive-xetex for PDF export).
+- v1.3.0: `:latest-studio-tex` variant (adds texlive-xetex for PDF export).
 
 ## v0.79.0 — 2026-06-08