chore: address Copilot review round 6

- verify-skills: the best-effort `plugin validate` hand-off now also requires
  the EXACT pinned CLI. `local:gate` runs `validate` before the pinned
  `verify:skills:cli` step, so a newer local CLI could reject skills that CI's
  pinned validator accepts — and the gate would exit there, never reaching the
  reproducible check. One schema everywhere, or none.
- Dropped `PLUGIN_VALIDATE_MIN_VERSION`: with both validators on the exact pin
  it was read only by its own test, and a constant nothing enforces is a claim
  nothing enforces. Its test now pins what actually matters — that equality is
  distinguishable from newer as well as older.
- The CI step's comment described the old floor behavior.
- issue-create: the duplicate check searched only open issues, so a completed or
  rejected match was invisible to a procedure that says never to duplicate.
  Searches all states and reports state/stateReason.

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

scripts/lib/skill-manifest.mjs

@@ -237,9 +237,6 @@ export function validateEvalCases(skillName, cases) {
  */
 export const PINNED_CLI_VERSION = "2.1.250";
 
-/** 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)").
  *