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).

.gitignore

@@ -262,3 +262,7 @@ skills-external/.higgsfield-stage.*/
 # ── gitflow standard socle (added by gitflow_init; additive, safe to edit) ──
 *.log
 !.claude/deploy/
+
+# mods/: the engine lays tsconfig.json beside a loaded mod; its
+# .claude-plugin/types/ ignores itself
+mods/*/tsconfig.json