✨ Add verify skill for the agent loop

A project-local Agent Skill (.agents/skills/verify/SKILL.md) wraps the
correctness ladder as an on-demand procedure: run npm run test, recover by
fixing the root cause in the types (not by suppressing them), optionally run
whole-project npm run check, and commit through the hook. Exposed as
/skill:verify for pi, and read by any Agent-Skills harness from .agents/skills/.

It is a procedure, not a doc fork: it links AGENTS.md / CONTRIBUTING.md /
package.json instead of restating the rules, so there is no drift.

Agents must not start `npm run watch` -- it never returns and blocks the turn.
The skill's ladder drops watch and calls it out under "What not to run here";
AGENTS.md gains a matching guardrail.

AGENTS.md

@@ -20,6 +20,8 @@ first-action facts. Do not restate evolving prose here — it will drift.
 
     The bot's definition of done: `npm run test` green, commit normally after.
 
+- A project skill wraps this loop as an on-demand procedure: `/skill:verify` → [`.agents/skills/verify/SKILL.md`](./.agents/skills/verify/SKILL.md).
+
 ## Never do
 
 Don't silence the type system to force a green run. As an agent these are forbidden:
@@ -32,6 +34,8 @@ Fix the root cause with the type system instead — narrowing, generics, `satisf
 
 The same applies to the checks themselves: **never `git commit --no-verify`** (or otherwise skip a pre-commit / pre-push hook). The checks are fast and offline, so a redundant run is fine — bypassing a hook to get green is the identical anti-pattern. If a commit already skipped a hook, redo it through one: `git reset --soft HEAD~1 && git commit -C <skipped-sha>`.
 
+Never start a long-lived / blocking process such as `npm run watch`. It runs until a human stops it with Ctrl-C, so in an agent turn it hangs forever and floods the context with continuous output. Reach for a one-shot command instead — `npm run test` (or `npm run check`) — to get feedback.
+
 ## Read these
 
 - [CONTRIBUTING.md § Rules the tools don't enforce](./CONTRIBUTING.md#rules-the-tools-dont-enforce) — the constraints the linters don't catch; CI/review bounce these. **The most important section.**