fix: brief template teaches runnable criteria; commands call validators through the plugin root

The skills reading (2026-10-06) found two defects the operator decided to fix
once wave 1 was merged:
- the brief template's Success Criteria examples used a pipe and npx, which
  the criteria runner refuses (and the brief validator now warns on);
- trekcontinue and trekexecute called lib/ scripts relative to the working
  directory, which is the user's repo, not the plugin.

Tests fail on the old text first (tests/lib/reading-defects.test.mjs).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

templates/trekbrief-template.md

@@ -109,8 +109,13 @@ Quantified where possible.*
 verifiable by running a specific command or observing a specific system behavior.*
 
 - {criterion — e.g., "All existing tests pass: `npm test` exits 0"}
-- {criterion — e.g., "New endpoint returns 200: `curl -s localhost:3000/api/health | jq .status` → `"ok"`"}
-- {criterion — e.g., "No TypeScript errors: `npx tsc --noEmit` exits 0"}
+- {criterion — e.g., "New endpoint answers ok: `bash tests/health.sh` exits 0 (the script calls the endpoint and checks the status field)"}
+- {criterion — e.g., "No TypeScript errors: `npm run typecheck` exits 0"}
+
+One command per criterion, from the runner's allowlist (`npm test`, `npm run <script>`,
+`node --test`, `pytest`, `bash tests/<script>.sh`, …), with no pipe or `&&`.
+Anything else is wrapped in a script under `tests/`; otherwise the review
+reports the criterion as NOT RUN.
 
 Do NOT write vague criteria:
 - "It should work" (not testable)