chore(ci): web workflow depends_on backend to serialize helm upgrades

.woodpecker/web.yaml

@@ -1,3 +1,11 @@
+# Depends on the backend workflow so that when a commit touches both
+# subtrees, web's helm upgrade waits for backend's. Avoids the helm release
+# lock race where two simultaneous `helm upgrade marktvogt` calls collide.
+# When only web/** changes (the common case), backend doesn't run and this
+# depends_on is a no-op.
+depends_on:
+  - backend
+
 when:
   - event: [push, pull_request]
     path: