fix: move workflows from .forgejo/workflows to .gitea/workflows

.forgejo/workflows/*.yaml never creates an action_run on push on this
Forgejo instance (1.27.0) -- confirmed directly in the action_run table
across multiple probe pushes. .gitea/workflows fires immediately with an
identical spec. This is why build.yaml never once executed.

.gitea/workflows/ci.yaml

@@ -0,0 +1,47 @@
+# Forgejo Actions CI — verification only (vet, test, build).
+# Build and push happens in build.yaml on main push.
+#
+# Path is .gitea/workflows/, not .forgejo/workflows/ or .github/workflows/.
+# Verified live against this instance (Forgejo 1.27.0, forgejo.riotpiao.com)
+# on 2026-08-21: a .forgejo/workflows/*.yaml file never creates an action_run
+# row on push, not once, for any repo -- confirmed both from application logs
+# (silent, no error) and directly in the action_run table. A .gitea/workflows
+# file with an identical job spec fires immediately. .github/workflows also
+# gets scanned (that's how the old, dead ubuntu-latest CI on this repo and on
+# kmsvc-manage both got action_run rows despite matching no runner) -- so
+# .forgejo/workflows/ specifically appears unsupported on this instance/version,
+# not workflow detection being off in general.
+#
+# runs-on: docker matches the only label the cluster runner declares.
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+    branches: [main]
+
+jobs:
+  verify:
+    name: Test, vet, build
+    runs-on: docker
+    container:
+      image: golang:1.25-bookworm
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: go vet
+        run: go vet ./...
+
+      # The race detector needs cgo, so this cannot run with CGO_ENABLED=0.
+      - name: go test -race
+        run: go test ./... -race
+
+      - name: Static build
+        run: CGO_ENABLED=0 go build -trimpath -o gateway ./cmd/gateway
+
+      - name: govulncheck
+        run: |
+          go install golang.org/x/vuln/cmd/govulncheck@latest
+          govulncheck ./...
+        continue-on-error: true