fix(linux): enable WebRTC in WebKitGTK; add Arch package build

WebKitGTK ships enable-media-stream/enable-webrtc off by default
(unlike WebView2/WKWebView), leaving navigator.mediaDevices undefined
and Element Call reporting "browser does not support WebRTC" on every
Linux build. Enable both settings and auto-grant the resulting
camera/mic permission request, mirroring the existing WebView2 handling.

Also add a build-arch CI job that repackages the existing .deb into a
real .pkg.tar.zst and uploads it to the Gitea release alongside the
Windows/Linux artifacts, for Arch/CachyOS users who'd rather use pacman
than an AppImage.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

.gitea/workflows/release.yml

@@ -281,6 +281,55 @@ jobs:
           upload "LotusChat-x86_64.AppImage.tar.gz.sig" "$APPIMAGE_DIR/Lotus Chat_${VERSION}_amd64.AppImage.tar.gz.sig"
           upload "LotusChat-x86_64.deb"                 "$DEB_DIR/Lotus Chat_${VERSION}_amd64.deb"
 
+  build-arch:
+    # Needs build-linux's .deb to already be on the release (this job
+    # downloads it from the fixed "latest" asset URL, same as update-manifest
+    # does for signatures) rather than recompiling from source.
+    needs: [prepare, build-linux]
+    runs-on: ubuntu-latest
+    container:
+      image: archlinux:base-devel
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install build tools
+        run: pacman -Syu --noconfirm --needed curl python
+
+      - name: Set package version
+        env:
+          VERSION: ${{ needs.prepare.outputs.version }}
+        run: sed -i "s/^pkgver=.*/pkgver=$VERSION/" packaging/pacman/PKGBUILD
+
+      - name: Build .pkg.tar.zst
+        run: |
+          # makepkg refuses to run as root. --nodeps: the package() step just
+          # extracts the .deb payload, so the runtime `depends` (webkit2gtk,
+          # gstreamer, ...) don't need to be installed on the build container.
+          useradd -m builder
+          chown -R builder:builder packaging/pacman
+          su builder -c 'cd packaging/pacman && makepkg -f --noconfirm --nodeps'
+
+      - name: Upload to release
+        env:
+          TOKEN: ${{ secrets.RELEASE_TOKEN }}
+          RELEASE_ID: ${{ needs.prepare.outputs.release_id }}
+        run: |
+          PKG=$(ls packaging/pacman/*.pkg.tar.zst)
+          NAME="LotusChat-x86_64.pkg.tar.zst"
+
+          existing_id=$(curl -sf "$GITEA_URL/api/v1/repos/$REPO/releases/$RELEASE_ID/assets" \
+            -H "Authorization: token $TOKEN" \
+            | python3 -c "import sys,json; assets=json.load(sys.stdin); print(next((str(a['id']) for a in assets if a['name']=='$NAME'), ''))" 2>/dev/null || true)
+          if [ -n "$existing_id" ]; then
+            curl -sf -X DELETE "$GITEA_URL/api/v1/repos/$REPO/releases/$RELEASE_ID/assets/$existing_id" \
+              -H "Authorization: token $TOKEN" || true
+          fi
+          curl -sf -X POST \
+            "$GITEA_URL/api/v1/repos/$REPO/releases/$RELEASE_ID/assets?name=$NAME" \
+            -H "Authorization: token $TOKEN" \
+            -H "Content-Type: application/octet-stream" \
+            --data-binary @"$PKG"
+
   update-manifest:
     needs: [prepare, build-windows, build-linux]
     runs-on: ubuntu-latest