feat(mods): model-router active in every session — skills-dir link, mods suite, doctor section, CLAUDE.md

Tracked relative symlink skills/model-router -> ../mods/model-router: Claude
Code loads the mod in place as model-router@skills-dir wherever link.sh
links ~/.claude/skills (no CLAUDE_CODE_PLUGIN_DIRS: absolute paths in the
tracked settings.json). Engine-laid mods/*/tsconfig.json gitignored.
lib/tests/mods.test.sh: manifest name, link target, claude plugin validate
and test per mod, capability-probed, time-bounded, SKIP with reason.
doctor.sh: fail-soft Mods section (link by -ef, one guarded plugin list).
CLAUDE.md: mods/ section (loading, per-machine enabled:false switch,
dev-copy shadowing, tests).

CLAUDE.md

@@ -59,6 +59,28 @@ Gotcha, learned the hard way: `git rm --cached` keeps the working file,
 but if the branch you merge into still tracks it, the merge deletes it
 from disk. Untrack and merge, then restore with the command above.
 
+## mods/ — function-hooks plugins (Claude Code mods)
+
+A mod lives in `mods/<name>/` (`.claude-plugin/plugin.json` + hooks). It
+loads through the tracked relative symlink `skills/<name>` -> `../mods/<name>`
+(`~/.claude/skills` links to `skills/`) as `<name>@skills-dir`, in place,
+live at the next session or `/reload-plugins`. New mod: `ln -s ../mods/<name>
+skills/<name>` from the repo root (guard with `[ -L ]`, a re-run nests a link).
+Not `CLAUDE_CODE_PLUGIN_DIRS` (absolute path, settings `env` has no `$HOME`
+expansion, settings.json is tracked), nor a local marketplace (`add` writes
+an absolute path into settings.json).
+- The engine lays `mods/<name>/tsconfig.json` and `.claude-plugin/types/`;
+  both are gitignored.
+- Optional user config: `~/.claude/<name>.json`. Its `"enabled": false` is the
+  per-machine off switch (untracked). `"<name>@skills-dir": false` in
+  `enabledPlugins` also works but lands in the TRACKED settings.json and
+  dirties every machine's tree.
+- A dev copy of the same name (`--plugin-dir`, hot-reload link in
+  `~/.claude/dev-mods/<session>/`) shadows the skills-dir copy for that
+  session: remove it before reading `/reload-plugins` as a test of the link.
+- Tests: `make test suite=lib/tests/mods.test.sh` (manifest, link,
+  `claude plugin validate`, `claude plugin test`). `doctor.sh` has a Mods section.
+
 ## Transient planning artifacts
 
 `docs/superpowers/specs/**` and `docs/superpowers/plans/**` are run-time