ci: add manual build workflow for testing artifacts

workflow_dispatch-triggered build.yml that produces Windows
installer/portable and Linux tarball as CI artifacts without
creating a release. Trigger from Gitea UI → Actions → Run.

.gitea/workflows/build.yml

@@ -0,0 +1,72 @@
+name: Build Artifacts
+
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'Version label (e.g. dev, 0.3.0-test)'
+        required: false
+        default: 'dev'
+
+jobs:
+  build-windows:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Build frontend
+        run: npm ci && npm run build
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+
+      - name: Install build tools
+        run: sudo apt-get update && sudo apt-get install -y --no-install-recommends nsis zip
+
+      - name: Build Windows distribution
+        run: |
+          chmod +x build-dist-windows.sh
+          ./build-dist-windows.sh "v${{ inputs.version }}"
+
+      - name: Build NSIS installer
+        run: makensis -DVERSION="${{ inputs.version }}" installer.nsi
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: MediaServer-${{ inputs.version }}-win-x64
+          path: |
+            build/MediaServer-*.zip
+            build/MediaServer-*-setup.exe
+          retention-days: 90
+
+  build-linux:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Build frontend
+        run: npm ci && npm run build
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+
+      - name: Build Linux distribution
+        run: |
+          chmod +x build-dist-linux.sh
+          ./build-dist-linux.sh "v${{ inputs.version }}"
+
+      - uses: actions/upload-artifact@v3
+        with:
+          name: MediaServer-${{ inputs.version }}-linux-x64
+          path: build/MediaServer-*-linux-x64.tar.gz
+          retention-days: 90