feat(effort): entry level on every skill next to its model pin (BDR-108)

- lib/effort-pins.txt (map) + lib/effort-pins.sh (idempotent re-apply)
  replace the hardcoded brainstorming/writing-plans loop; called after the
  last vendoring step of install-plugins.sh AND update-all.sh (the resync
  dropped the pins until the next make plugin)
- design stack high uniform (last loaded wins), superpowers, agent-skills,
  21st pack pinned from the map; skills-perso low, pdf-translate medium,
  site-motion high
- doctrine: design stack loads paired with the first Read; one level per
  stack (CLAUDE.global.md, lib/effort-shift.md)
- lib/effort-audit.py prints thinking coverage per scope (sub-agent records
  carry no thinking count on ~94 % of requests)
- census map-driven + fixture suite lib/tests/effort-pins.test.sh; docs
  README/USAGE/CHANGELOG; contract + TODO plan

lib/effort-shift.md

@@ -24,6 +24,11 @@ max (stuck error, judged need).
   Claude loads alone, such as `brainstorming` or `writing-plans`, applies
   nothing). Last loaded wins, both directions. The prompt cache survives a
   shift.
+- **Stacked skills share one level**: skills that load together in one
+  build (the design stack) all pin the same level, since the last loaded
+  wins. Vendored externals get their level from `lib/effort-pins.txt`,
+  re-applied by `lib/effort-pins.sh` after every vendoring step; repo
+  skills carry it in their frontmatter.
 - Dispatched agents run on their own `effort:` pin, never on a shift.
   Unpinned agents inherit the level in force at dispatch.
 - Headless sessions (`-p`, `claude agents`, SDK) ignore skill-level effort: