feat(ci): add scheduled auto-release workflow

Introduce a cron-triggered auto-release workflow that runs on the second Sunday of each month,
creating a time-based tag in YYYY-MM format and dispatching the release workflow.

The release workflow is extended with a workflow_dispatch trigger accepting a tag input, so it can be
invoked both by tag pushes and programmatically by the auto-release. Version extraction is unified
via a dedicated step using `inputs.tag || github.ref_name` in both jobs.

Co-authored-by: Copilot <copilot@github.com>

.gitea/workflows/release.yaml

@@ -4,12 +4,34 @@ on:
   push:
     tags:
     - "**"
+  workflow_dispatch:
+    inputs:
+      tag:
+        description: "Tag which should be released"
+        type: string
+        required: true
 
 jobs:
   push-arch-linux:
     runs-on: ubuntu-latest-amd64
     steps:
+      - id: version_extraction
+        name: Extract git tag
+        run: |
+          VERSION="${{ inputs.tag || github.ref_name }}"
+          VERSION="${VERSION#refs/*/}"
+
+          echo "Version (raw):      ${VERSION}"
+          echo "Version (cleaned):  ${VERSION/v/}"
+
+          echo "version_raw=${VERSION}" >> $GITHUB_OUTPUT
+          echo "version_cleaned=${VERSION/v/}" >> $GITHUB_OUTPUT
+
       - uses: actions/checkout@v4.2.2
+        with:
+          fetch-tags: true
+          ref: "${{ steps.version_extraction.outputs.version_raw }}"
+
       - uses: docker/setup-qemu-action@v3.6.0
       - uses: docker/setup-buildx-action@v3.10.0
 
@@ -21,7 +43,7 @@ jobs:
 
       - name: Build and push image
         run: |
-          TAG=$(echo ${{ github.ref_name }} | sed 's/v//gm')
+          TAG=${{ steps.version_extraction.outputs.version_cleaned }}
 
           docker buildx build \
             --file Dockerfile.archlinux \
@@ -34,9 +56,17 @@ jobs:
     - push-arch-linux
     runs-on: ubuntu-latest
     steps:
+    - id: version_extraction
+      name: Extract git tag
+      run: |
+        VERSION="${{ inputs.tag || github.ref_name }}"
+        VERSION="${VERSION#refs/*/}"
+
+        echo "version_cleaned=${VERSION/v/}" >> $GITHUB_OUTPUT
+
     - name: Copy images to docker.io
       run: |
-        TAG=$(echo ${{ github.ref_name }} | sed 's/v//gm')
+        TAG=${{ steps.version_extraction.outputs.version_cleaned }}
 
         apt-get update --yes
         apt-get install --yes skopeo