feat: Phase 4 — reusable "subscribe" workflow (+ dogfood it) (#8)

Centralizes the consumer stub into a reusable Gitea workflow
(.gitea/workflows/review-reusable.yml, workflow_call + defaulted inputs +
secrets: inherit); gadfly's own dogfood is now a thin caller of it, which
proved end-to-end that github.event context propagates into the reusable
on this act_runner. Adds the slim examples/reusable.yml stub + docs.

Folded in the swarm's findings: timeout_minutes default 30->45, map
GADFLY_API_KEY, explicit permissions block, drop the dead specialist_suite
input, and harden the example's actor gate. ~70 findings graded.

Completes the gadfly-games build (Phases 1-4 + quality fixes).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Co-authored-by: Steve Dudenhoeffer <steve@stevedudenhoeffer.com>
Co-committed-by: Steve Dudenhoeffer <steve@stevedudenhoeffer.com>

CLAUDE.md

@@ -46,6 +46,9 @@ entrypoint.sh          container brains: trigger gating, PR clone, model loop (t
                        used to live in workflow YAML)
 Dockerfile             multi-stage; private-module creds via BuildKit secrets never reach the final image
 .gitea/workflows/build-image.yml   push main → :latest; tag v* → :<tag>+:latest; PR → build-only
+.gitea/workflows/review-reusable.yml  reusable (workflow_call) review job; consumers subscribe with
+                       an ~8-line caller + `secrets: inherit` (Phase 4). gadfly's own
+                       adversarial-review.yml is a thin caller of it (dogfoods the path).
 examples/              copy-paste consumer stub workflows for different providers
 ```