chore(skills): wire agent/skills to the skills CLI global store

Retroactive provenance registration: the 10 pi-era skill snapshots are
byte-identical to upstream (38 skills mattpocock/skills + find-skills
vercel-labs/skills), now canonically installed at ~/.agents/skills with
store lockfile ~/.agents/.skill-lock.json (39 entries, folder hashes).

omp is not a skills-CLI agent id, so the omp tier becomes manual wiring:
replace the 10 tracked skill directories with symlinks into the store
and link the remaining 29 upstream skills the same way (39 links). The
repo now records the enabled set, never content; skills update -g
propagates through the links. managed-skills tier untouched.

Docs: skill-store-wiring.md (+index). Snapshot of the old real dirs at
/tmp/agent-skills-snap-20261018 for the transition window.

agent/skills/pr

@@ -0,0 +1 @@
+/home/blank/.agents/skills/pr