Add CalVer build-time version tracking

- Dockerfile: ARG BUILD_VERSION=dev → ENV APP_VERSION baked into image
- ci.yml: BUILD_VERSION passed as build-arg; set to git tag name on v*
  tag builds, "dev" on branch builds
- routes/api.py: GET /api/version returns {"version": APP_VERSION}
- SettingsView: fetches /api/version on mount, displays in About section
  under General tab

Version source of truth is the git tag (YY.MM.DD.N CalVer).
pyproject.toml / package.json versions are no longer maintained.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.forgejo/workflows/ci.yml

@@ -104,18 +104,21 @@ jobs:
     steps:
       - uses: actions/checkout@v6
 
-      - name: Generate image tags
+      - name: Generate image tags and version
         id: tags
         run: |
           TAGS="${{ env.IMAGE }}:${{ github.sha }}"
+          BUILD_VERSION="dev"
           if [[ "${{ github.ref }}" == "refs/heads/main" ]]; then
             TAGS="$TAGS,${{ env.IMAGE }}:latest"
           elif [[ "${{ github.ref }}" == "refs/heads/dev" ]]; then
             TAGS="$TAGS,${{ env.IMAGE }}:dev"
           elif [[ "${{ github.ref }}" == refs/tags/* ]]; then
             TAGS="$TAGS,${{ env.IMAGE }}:latest,${{ env.IMAGE }}:${{ github.ref_name }}"
+            BUILD_VERSION="${{ github.ref_name }}"
           fi
           echo "value=$TAGS" >> $GITHUB_OUTPUT
+          echo "build_version=$BUILD_VERSION" >> $GITHUB_OUTPUT
 
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v4
@@ -133,5 +136,6 @@ jobs:
           context: .
           push: true
           tags: ${{ steps.tags.outputs.value }}
+          build-args: BUILD_VERSION=${{ steps.tags.outputs.build_version }}
           cache-from: type=registry,ref=${{ env.IMAGE }}:cache
           cache-to: type=registry,ref=${{ env.IMAGE }}:cache,mode=max