Add layered environment model and taskfile composition rules

Fold two overlapping local skills (scripts-shell, shell-scripts-module)
into this one, keeping only what it did not already cover.

- Add references/environment-model.md: the three-layer .env selector model,
  why set -a dot-sourcing beats export $(grep|xargs), tracked samples, the
  no-re-sourcing rule for module readers, and the deployment boundary
  (repo-presence is not git-tracked is not deployed).
- Extend references/taskfile.md with the one-env-driven-task rule (no
  :default pairs) and composing commands through the task surface.
- Add the lifecycle-hook module type to references/module-patterns.md.
- Keep this skill's _moduleExampleV1_ naming as canonical; the retired
  skills' HL_V1_ and double-underscore dialects were not carried over.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

references/module-patterns.md

@@ -13,6 +13,14 @@ others.
 | Shared foundation with public commands | Yes | Optional / no | `base` |
 | Feature module | Yes | Usually yes | `kube`, `github`, `data-migration` |
 | Wrapper around an external CLI | Yes | Usually yes | `helm`, `openshift`, `github` |
+| Lifecycle hook | Yes | No | `devbox` (an `on-init-hook`) |
+
+A **lifecycle hook** module is invoked by external tooling at a fixed moment — a devbox init
+hook, a container entrypoint, a git hook — rather than by an operator. It keeps `api/` because
+the tool calls that path directly, and skips `Taskfile.yml` because nobody runs it by hand.
+Its implementation commonly branches per platform (`-install-dependencies-osx.sh`,
+`-install-dependencies-linux-ubuntu.sh`), one file per branch, sourced from `--index-api.sh`
+like any other implementation file.
 
 Pick the type before creating any file — it decides whether `api/` and `Taskfile.yml` exist at
 all, and adding them later means reworking every consumer that has already started sourcing