ci: allow manual Tests runs on main via workflow_dispatch

A GitHub Actions outage on 2026-08-06 dropped the push triggers for
several merges to main, so main-HEAD carries no Tests conclusion. Heart's
ws_ci gate reads main-HEAD conclusions, so missing evidence blocks a
release just as a red run would.

Re-running an existing run re-tests that run's own (older) sha, so the
only recovery was pushing an empty commit to main. Adding
workflow_dispatch makes a main-HEAD run re-requestable on demand.

No change to what is tested or when it runs automatically.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MhmtTYYG4BianpWFSffZKN

Author: claude

.github/workflows/main.yml

@@ -4,10 +4,18 @@ name: Tests
 # (Heart's ws_ci gate reads main-HEAD conclusions). Superseded runs are
 # cancelled on PR refs only — a cancelled main run would read as red CI
 # (cancelled is in Heart's FAILURE_CONCLUSIONS).
+#
+# `workflow_dispatch` exists so a main-HEAD run can be re-requested on demand.
+# On 2026-08-06 a GitHub Actions outage dropped the push triggers for several
+# main merges, leaving main-HEAD with no Tests conclusion at all — which reads
+# to Heart's ws_ci gate as missing evidence and blocks a release. Without a
+# manual trigger the only recovery was an empty commit to main, since re-running
+# an existing run re-tests its own (older) sha.
 on:
   push:
     branches: [main]
   pull_request:
+  workflow_dispatch:
 
 concurrency:
   group: main-${{ github.ref }}