chore: address Copilot review round 2

- verify-skills: version-gate the optional `claude plugin validate`. Probing
  only for the executable failed the MANDATORY gate for anyone on a CLI older
  than 2.1.233, which has no such subcommand and exits nonzero on it. Skips
  below the floor; a failure now means a supported validator rejected the skills.
- skill-eval: match the invoked skill structurally. A substring test counted
  `{"skill":"not-testing"}` as a hit for `testing` and inflated the rate.
- skill-eval: `runOnce` → exported `runPrompt` with an injectable `spawnFn`, so
  the nonzero-exit branch is actually pinned. Reverting it now fails a test
  (verified by mutation) rather than leaving the suite green.
- board-ops: filter the item lookups by repository. Issue numbers are repo-local
  and these are org boards — #11 really does carry a `servers` card — so an
  unfiltered `select` can move or delete the wrong card, or pass two ids.
- issue-triage: the audit's `own()` filter dropped draft cards, which carry no
  `.content.repository`, so the "non-Issue on a board" check reported 0 while
  the invariant was being violated. Verified against a fixture.
- pr-flow: cut the branch from the base it will target. The blanket "cut from
  v2/main" was wrong for v1, whose history is unrelated.

Signed-off-by: cliffhall <cliff@futurescale.com>

scripts/lib/skill-manifest.mjs

@@ -206,3 +206,30 @@ export function validateEvalCases(skillName, cases) {
   }
   return errors;
 }
+
+/** First Claude Code release with `claude plugin validate`. */
+export const PLUGIN_VALIDATE_MIN_VERSION = [2, 1, 233];
+
+/**
+ * Read a semver triple out of `claude --version` output ("2.1.250 (Claude Code)").
+ *
+ * @param {string} text
+ * @returns {number[] | null}
+ */
+export function parseClaudeVersion(text) {
+  const m = /(\d+)\.(\d+)\.(\d+)/.exec(text);
+  return m === null ? null : [Number(m[1]), Number(m[2]), Number(m[3])];
+}
+
+/**
+ * @param {number[]} a
+ * @param {number[]} b
+ * @returns {number} negative if a < b, 0 if equal, positive if a > b.
+ */
+export function compareVersions(a, b) {
+  for (let i = 0; i < Math.max(a.length, b.length); i++) {
+    const diff = (a[i] ?? 0) - (b[i] ?? 0);
+    if (diff !== 0) return diff;
+  }
+  return 0;
+}