fix(ci): move workflow to .gitea/workflows — the server is Gitea, not Forgejo

The runner was alive all along (gitea/act_runner, ubuntu-latest label);
no run ever appeared because Gitea only reads .gitea/workflows/ (or
.github/workflows/) and ignores the .forgejo/ path the workflow shipped
under. The legacy repo's .gitea/workflows/check.yml was the clue.
References corrected (workflow header, TESTING.md, agent files); this
push doubles as the first live trigger of the workflow.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/TESTING.md

@@ -24,8 +24,8 @@ so template/wrapper drift fails fast too.
 
 ## 1b. CI (automatic on push)
 
-Every push to `main`/`v1` runs `.forgejo/workflows/check.yml`: the §1
-cheap checks (flake eval, Python + shell syntax) on the Forgejo instance.
+Every push to `main`/`v1` runs `.gitea/workflows/check.yml`: the §1
+cheap checks (flake eval, Python + shell syntax) on the Gitea instance.
 That's the **eval tier only** — the runner is a docker container without
 KVM, so the `checks.*` VM suite and real builds stay local (this file)
 until a KVM-capable runner is registered; the workflow carries a