feat: add Gitea CI workflow for cross-compiling Windows desktop client on Linux

Add workflow to build Windows desktop client using cargo-xwin on Linux runners. Install Node.js 22, Rust with x86_64-pc-windows-msvc target, and required system dependencies including NSIS for installer creation. Build bundled Windows tunnel helper and desktop client installer, then upload both NSIS installer artifacts and raw executables.

.gitea/workflows/windows-desktop-client.yml

@@ -0,0 +1,85 @@
+name: Build Windows Desktop Client
+
+on:
+  workflow_dispatch:
+  push:
+    branches:
+      - main
+      - master
+    paths:
+      - ".gitea/workflows/windows-desktop-client.yml"
+      - "desktop-client/**"
+
+jobs:
+  build-windows-client:
+    name: Build Windows Client
+    runs-on:
+      - self-hosted
+      - linux
+
+    defaults:
+      run:
+        shell: bash
+        working-directory: desktop-client
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Setup Node.js
+        uses: actions/setup-node@v4
+        with:
+          node-version: "22"
+
+      - name: Install Rust toolchain
+        uses: dtolnay/rust-toolchain@stable
+        with:
+          targets: x86_64-pc-windows-msvc
+
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y \
+            build-essential \
+            curl \
+            wget \
+            file \
+            nsis \
+            pkg-config \
+            libssl-dev \
+            libayatana-appindicator3-dev \
+            librsvg2-dev \
+            patchelf
+
+      - name: Install cargo-xwin
+        run: |
+          if ! cargo xwin --version >/dev/null 2>&1; then
+            cargo install --locked cargo-xwin
+          fi
+
+      - name: Install desktop client dependencies
+        run: npm install
+
+      - name: Build bundled Windows tunnel helper
+        run: npm run helper:windows-x64
+
+      - name: Build Windows installer
+        run: npm run tauri:build:windows-x64:linux
+
+      - name: Upload Windows installer
+        uses: christopherhx/gitea-upload-artifact@v4
+        with:
+          name: NexaVPN-windows-installer
+          path: |
+            desktop-client/src-tauri/target/x86_64-pc-windows-msvc/release/bundle/nsis/*.exe
+            desktop-client/src-tauri/target/x86_64-pc-windows-msvc/release/bundle/nsis/*.msi
+          if-no-files-found: error
+
+      - name: Upload raw Windows build outputs
+        uses: christopherhx/gitea-upload-artifact@v4
+        with:
+          name: NexaVPN-windows-raw-build
+          path: |
+            desktop-client/src-tauri/target/x86_64-pc-windows-msvc/release/nexavpn-desktop.exe
+            desktop-client/src-tauri/bundled/windows-x64/nexavpn-tunnel-helper.exe
+          if-no-files-found: error