ci: serialize ci-deploy runs on pve-201 to prevent docker name race

Two near-simultaneous pushes both hit `docker stop/rm/run flights-web`,
the second run failed with 'container name already in use'. Add a Gitea
Actions concurrency group so subsequent runs queue behind the in-flight
one rather than racing.

.gitea/workflows/ci-deploy.yml

@@ -5,6 +5,14 @@ on:
     branches: [main]
   workflow_dispatch:
 
+# Single deploy at a time per host — pve-201's docker container name
+# `flights-web` is a shared mutex. Without this, back-to-back pushes
+# race on `docker stop / rm / run`, with the second run hitting
+# "container name already in use". Queue, don't cancel.
+concurrency:
+  group: ci-deploy-pve-201
+  cancel-in-progress: false
+
 jobs:
   build-deploy-test:
     runs-on: ubuntu-latest