fix(kyberforge): stop the content mirror amputating a shipped template asset

The mirror's `tests/` exclusion was depth-agnostic, so it deleted
`skill-author/assets/templates/tests/` — a template the skill scaffolds FROM —
alongside the depth-2 dev fixtures it was meant to drop. Since ADR-0017 makes the
mirror the installed content, the shipped scaffolder was broken: the mirror copy of
`new-skill.sh` exited 2 on `sed: can't read .../tests/README.md`, leaving a
half-written skill, while the byte-identical `.apm/` copy exited 0. `--check` was
green about it.

Check mode was restructured rather than patched because `diff -x` matches a basename
at any depth and cannot express the depth-2 scoping the fix needs — the two modes
could not be made to agree by construction. Check mode now runs the real `sync_dir`
into a throwaway root and diffs with no exclusions, leaving the exclusion rule and
the hooks destination each in exactly one place.

Also fixed here, all previously invisible to `--check`:

- Merged hooks were written to `<plugin>/hooks.json`, which Claude Code does not
  convention-scan, while ADR-0017 itself quoted `hooks/hooks.json` as the contract.
  Moved, with the legacy path cleaned up as stale. No `hooks` pointer is added to
  `plugin.json`, so this does not reopen the option ADR-0017 rejected.
- Only the first drift per plugin was reported: `diff | sed` returns 1 under
  `pipefail`, and `set -e` killed the subshell before the remaining checks and
  before `FAIL=1`.
- File-mode and symlink drift were invisible, so `--check` and a real sync
  disagreed; a find-based type/mode manifest now covers both.

The tests pinned almost none of this — the stale-skill wipe, the check-mode stale
branch, three `MIRROR_DIRS` entries and the hooks newline normalization could each
be deleted with the suite still green. All are now mutation-tested.

Refs: #90
ADR: 0017

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01X7GvKuJfy2WrdBmUttV4DT

plugins/kyberforge/skills/skill-author/assets/templates/tests/README.md

@@ -0,0 +1,33 @@
+# tests/
+
+Test files for scripts bundled with this skill.
+
+## When to add tests
+
+Add tests here when the skill has scripts in `scripts/` that are complex enough
+to break silently — validators, parsers, generators, anything with branching
+logic or edge cases. Test infrastructure (`.bats`, `*_test.*`, `test_*.sh`)
+belongs here, not in `scripts/`.
+
+## Dependencies
+
+Tests require [bats-support](https://github.com/bats-core/bats-support) and
+[bats-assert](https://github.com/bats-core/bats-assert). The test files load
+helpers from the repo root's `tests/test_helper/`.
+
+From the repo root:
+
+```bash
+git clone https://github.com/bats-core/bats-support tests/test_helper/bats-support
+git clone https://github.com/bats-core/bats-assert tests/test_helper/bats-assert
+```
+
+Run all tests for this skill (from the repo root):
+
+```bash
+bats <destination-dir>/SKILL_NAME/tests/
+```
+
+## If no tests are needed
+
+Delete this README and the `tests/` directory entirely.