Add GitHub Actions workflow to build Linux x64 deps

Workflow_dispatch that installs build tools, runs download-deps-linux.sh
to compile Python/VapourSynth/FFmpeg/plugins from source, packages the
zip, and optionally uploads to a GitHub release.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: StuartCameronCode

.github/workflows/build-deps-linux.yml

@@ -0,0 +1,54 @@
+name: Build Linux Deps
+
+on:
+  workflow_dispatch:
+    inputs:
+      version:
+        description: 'Deps version (e.g., 1.3.0)'
+        required: true
+        type: string
+      release_tag:
+        description: 'Upload to this release tag (e.g., deps-v1.3.0). Leave empty to skip upload.'
+        required: false
+        type: string
+
+jobs:
+  build-deps:
+    runs-on: ubuntu-22.04
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v4
+
+      - name: Install build dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y \
+            meson ninja-build cmake nasm patchelf autoconf automake libtool \
+            cython3 pkg-config gcc g++ \
+            libfftw3-dev libboost-filesystem-dev libboost-atomic-dev \
+            ocl-icd-opencl-dev opencl-headers libdvdread-dev \
+            unzip
+
+      - name: Build dependencies
+        run: |
+          ./Scripts/download-deps-linux.sh --force
+
+      - name: Package dependencies
+        run: |
+          ./Scripts/package-deps-linux.sh --version "${{ inputs.version }}" --arch x64
+
+      - name: Upload artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: VapourBox-deps-${{ inputs.version }}-linux-x64
+          path: dist/VapourBox-deps-${{ inputs.version }}-linux-x64.zip
+
+      - name: Upload to release
+        if: ${{ inputs.release_tag != '' }}
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          gh release upload "${{ inputs.release_tag }}" \
+            "dist/VapourBox-deps-${{ inputs.version }}-linux-x64.zip" \
+            --clobber