ci: add GitHub Actions workflow for Linux build (.deb + .AppImage)

- Triggers on workflow_dispatch (manual) or version tag push (v*)
- Ubuntu 22.04 runner with Tauri prerequisites
- Uploads .deb and .AppImage as artifacts
- Creates GitHub Release on tag push

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

posimai-guard-app/.github/workflows/build-linux.yml

@@ -0,0 +1,72 @@
+name: Build Linux
+
+on:
+  workflow_dispatch:   # 手動実行
+  push:
+    tags:
+      - 'v*'           # v1.0.0 など tag push で自動実行
+
+jobs:
+  build-linux:
+    runs-on: ubuntu-22.04
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y \
+            libwebkit2gtk-4.1-dev \
+            libappindicator3-dev \
+            librsvg2-dev \
+            patchelf \
+            libssl-dev \
+            libgtk-3-dev \
+            libayatana-appindicator3-dev
+
+      - name: Install Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache Rust
+        uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: src-tauri
+
+      - name: Install Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Install npm dependencies
+        run: npm install
+
+      - name: Build Tauri (Linux)
+        run: npm run build
+        env:
+          TAURI_SIGNING_PRIVATE_KEY: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY }}
+          TAURI_SIGNING_PRIVATE_KEY_PASSWORD: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY_PASSWORD }}
+
+      - name: Upload .deb
+        uses: actions/upload-artifact@v4
+        with:
+          name: posimai-guard-linux-deb
+          path: src-tauri/target/release/bundle/deb/*.deb
+          if-no-files-found: warn
+
+      - name: Upload .AppImage
+        uses: actions/upload-artifact@v4
+        with:
+          name: posimai-guard-linux-appimage
+          path: src-tauri/target/release/bundle/appimage/*.AppImage
+          if-no-files-found: warn
+
+      - name: Create GitHub Release (on tag)
+        if: startsWith(github.ref, 'refs/tags/')
+        uses: softprops/action-gh-release@v2
+        with:
+          files: |
+            src-tauri/target/release/bundle/deb/*.deb
+            src-tauri/target/release/bundle/appimage/*.AppImage
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}