docs: add repo CLAUDE.md forbidding worktree development

The plugin installs via symlinks pinned at the absolute path of the
primary clone, so skill/agent/workflow edits made in a git worktree of
this repo are not what the live session runs (silent no-op or, on
re-install, a split-brain). Record a no-worktree rule for this repo in a
repo-local CLAUDE.md, with the dominant symlink-pinning rationale plus
the secondary cwd-slug memory/transcript re-keying caveat.

closes #15

CLAUDE.md

@@ -0,0 +1,31 @@
+# Skills plugin — repo-local rules
+
+This is the skills plugin's own repository. It does not consume its own
+pipeline: there is no `## Skills plugin: project facts` section and no
+per-cycle skill dispatch here. Changes are made directly and committed to
+`main`.
+
+## Do not develop this repo from a git worktree
+
+Never work on this repository from a git worktree — neither a manual
+`git worktree add` nor the harness `EnterWorktree` tool. Always edit the
+primary clone at `~/dev/skills`, on `main`.
+
+Reason (dominant): `install.sh` installs the plugin by symlinking
+`~/.claude/{skills,agents,workflows}` to the absolute path of the clone it
+was first run from — the primary clone. A running session loads every
+skill, agent, and workflow definition through those symlinks regardless of
+cwd, so it always executes the primary clone's bodies. Edits made in a
+worktree of this repo are therefore not what the live session runs:
+dispatching an edited skill silently runs the old primary-clone body, and
+re-running `install.sh` from a worktree skips the existing symlinks and
+only adds links for new skills (a split-brain across two checkouts).
+Worktree development of the plugin is silently ineffective.
+
+Secondary: a worktree session also re-keys the cwd-derived project slug,
+so the accumulated auto-memory and the session transcript land under a
+different namespace than the primary clone.
+
+This constraint is specific to editing the plugin itself. Consumer
+projects are unaffected: they resolve the same global symlinks and read
+their own checked-in `CLAUDE.md`, so they may use worktrees freely.