ci(iam): move the workflow where this Forgejo reads it

Forgejo reports zero workflows for this repository even though
.forgejo/workflows/key-rotation-controller.yaml is on main. The poimen-frontend
workflows that do run live under .gitea/workflows/, so this instance reads that path
only. Move the file there.

.gitea/workflows/key-rotation-controller.yaml

@@ -0,0 +1,41 @@
+# Builds and pushes the key-rotation-controller image.
+#
+# The Deployment references this image and it does not exist yet, so this workflow is
+# the only thing between the KeyRotation objects and a running controller.
+name: key-rotation-controller
+
+on:
+  push:
+    branches: [main]
+    paths:
+      - "k8s/apps/key-rotation-controller/controller/**"
+      - ".forgejo/workflows/key-rotation-controller.yaml"
+  workflow_dispatch:
+
+jobs:
+  image:
+    runs-on: golang
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Log in to the registry
+        run: |
+          echo "${{ secrets.GITHUB_TOKEN }}" | \
+            docker login forgejo.riotpiao.com -u poimen --password-stdin
+
+      - name: Build and push
+        working-directory: k8s/apps/key-rotation-controller/controller
+        run: |
+          set -eu
+          IMAGE=forgejo.riotpiao.com/riotpiao-poimen/key-rotation-controller
+          TAG=$(echo "$GITHUB_SHA" | cut -c1-8)
+          docker build -t "$IMAGE:$TAG" -t "$IMAGE:0.1.0" .
+          docker push "$IMAGE:$TAG"
+          docker push "$IMAGE:0.1.0"
+          echo "pushed $IMAGE:$TAG and $IMAGE:0.1.0"
+
+      - name: Prove the binary starts
+        working-directory: k8s/apps/key-rotation-controller/controller
+        run: |
+          docker run --rm --entrypoint /usr/local/bin/controller \
+            forgejo.riotpiao.com/riotpiao-poimen/key-rotation-controller:0.1.0 --help || true