feat(v2): add packaging, installer, and CI release workflow (Phase 6)

Build-from-source installer (install-v2.sh) with dependency checks for
Node.js 20+, Rust 1.77+, and system libraries. Tauri bundle config for
.deb and AppImage targets. GitHub Actions workflow builds and uploads
release artifacts on version tags. Icons regenerated as RGBA PNGs.

.github/workflows/release.yml

@@ -0,0 +1,104 @@
+name: Release
+
+on:
+  push:
+    tags:
+      - "v*"
+
+permissions:
+  contents: write
+
+env:
+  CARGO_TERM_COLOR: always
+
+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 \
+            libgtk-3-dev \
+            libayatana-appindicator3-dev \
+            librsvg2-dev \
+            libssl-dev \
+            build-essential \
+            pkg-config \
+            curl \
+            wget \
+            libfuse2
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: 20
+          cache: npm
+          cache-dependency-path: v2/package-lock.json
+
+      - name: Setup Rust
+        uses: dtolnay/rust-toolchain@stable
+
+      - name: Cache Rust dependencies
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+            v2/src-tauri/target
+          key: ${{ runner.os }}-cargo-${{ hashFiles('v2/src-tauri/Cargo.lock') }}
+          restore-keys: |
+            ${{ runner.os }}-cargo-
+
+      - name: Install npm dependencies
+        working-directory: v2
+        run: npm ci --legacy-peer-deps
+
+      - name: Build Tauri app
+        working-directory: v2
+        run: npx tauri build
+
+      - name: List build artifacts
+        run: |
+          find v2/src-tauri/target/release/bundle -type f \( -name "*.deb" -o -name "*.AppImage" \) | head -20
+
+      - name: Upload .deb
+        uses: actions/upload-artifact@v4
+        with:
+          name: bterminal-deb
+          path: v2/src-tauri/target/release/bundle/deb/*.deb
+
+      - name: Upload AppImage
+        uses: actions/upload-artifact@v4
+        with:
+          name: bterminal-appimage
+          path: v2/src-tauri/target/release/bundle/appimage/*.AppImage
+
+  release:
+    needs: build-linux
+    runs-on: ubuntu-22.04
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Download .deb
+        uses: actions/download-artifact@v4
+        with:
+          name: bterminal-deb
+          path: artifacts/
+
+      - name: Download AppImage
+        uses: actions/download-artifact@v4
+        with:
+          name: bterminal-appimage
+          path: artifacts/
+
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v2
+        with:
+          generate_release_notes: true
+          files: |
+            artifacts/*.deb
+            artifacts/*.AppImage