fix(ci): drop duplicate concurrency block from spark-theatre-gate caller (closes #438)

PR #379 (2026-05-27) added a workflow-level `concurrency:` block to this
caller as part of "add concurrency blocks to 5 read-only workflows". The
spark-theatre-gate reusable workflow in standards already declares the
SAME concurrency key — and `${{ github.workflow }}` in a reusable
resolves to the CALLER'S workflow name (per the estate-known reusable
caller-context-vars semantics).

Stacking both blocks causes GitHub to reject the run at workflow-
creation time with a `startup_failure`. The Actions UI shows the run
as failed in 2s, but no job ever spins up and no `check_run` is ever
emitted — so the required status-check context
`spark-theatre-gate / SPARK Theatre Gate` stays unsatisfied on every
PR.

Empirical signature: every spark-theatre-gate run before 2026-05-27
13:16Z (when #379 merged) is `success` or concurrency-`cancelled`;
every run after is `failure`/`startup_failure` with `run_duration_ms`
≈ 2000 and zero jobs.

This was the root cause of every affinescript PR sitting in
`mergeStateStatus: BLOCKED` despite all visible checks passing — and
of the 14-PR admin-merge sweep on 2026-05-28. Closes #438.

Cross-reference: hypatia#376 (BP008 phantom-required-context detector
+ AM010 admin-merge eligibility) makes this class of failure visible
estate-wide going forward.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

.github/workflows/spark-theatre-gate.yml

@@ -13,11 +13,17 @@ on:
 permissions:
   contents: read
 
-# Actions concurrency pool. Applied only to read-only check workflows
-# (no publish/mutation), so cancelling a superseded run is always safe.
-concurrency:
-  group: ${{ github.workflow }}-${{ github.ref }}
-  cancel-in-progress: true
+# Note: NO workflow-level `concurrency:` block here. The reusable
+# workflow in standards already declares concurrency on the same key
+# (`${{ github.workflow }}-${{ github.ref }}` — which resolves to the
+# CALLER'S workflow name in reusables). Stacking both blocks causes
+# GitHub to reject the workflow at run-creation time with a
+# `startup_failure`, so no `check_run` is ever emitted and every PR's
+# required `spark-theatre-gate / SPARK Theatre Gate` context stays
+# unsatisfied. Empirically: PR #379 (2026-05-27) added this block; all
+# 410+ runs since have been `startup_failure`, blocking auto-merge
+# across the repo and forcing a 14-PR admin-merge sweep on
+# 2026-05-28. See hypatia#376 BP008 for the class-level detector.
 
 jobs:
   spark-theatre-gate: