chore(skills): move upstream skills to the CLI global store, keep authored tier

Retroactive provenance: the 10 pi-era skill snapshots were byte-identical
to upstream. Canonical installs now live in ~/.agents/skills tracked by
~/.agents/.skill-lock.json (mattpocock/skills x38 after grilling removal,
find-skills from vercel-labs/skills).

Repo tier is authored overrides only: clear all 10 tracked upstream
snapshots; omp loads the store directly through the agents provider
(skills.enableAgentsUser, default on). grilling returns as a real
directory — extracted from the store (CLI + lockfile pruned) so Frank can
customize it without skills update resurrecting a twin.

Docs: skill-store-wiring.md (+index). Pre-cutover snapshot of the old
tracked dirs at /tmp/agent-skills-snap-20261018.

agent/skills/grilling/SKILL.md

@@ -3,6 +3,8 @@ name: grilling
 description: Grill the user relentlessly about a plan, decision, or idea. Use when the user wants to stress-test their thinking, or uses any 'grill' trigger phrases.
 ---
 
+> **Authored override.** Extracted 2026-10-18 from `mattpocock/skills` (identical to upstream at extraction) into the command-center repo so Frank can customize it. Removed from the `skills` CLI global store (`~/.agents/.skill-lock.json` pruned) so `skills update -g` never resurrects a duplicate. Edits to this file are repo prose: branch → PR → Frank OK.
+
 Interview the user relentlessly until you reach a shared understanding. Map this as a **design tree**: every decision branches into the decisions that hang off it.
 
 Work the tree in **rounds**. The **frontier** is every decision whose prerequisites are already settled: the questions you can ask _now_ without guessing at answers you haven't heard yet. Ask the whole frontier in one round: number each question and give your recommended answer. Then wait for the user's answers before the next round.