fix: use pre-installed Rust to avoid static.rust-lang.org connection failures

The Linux runner cannot reach static.rust-lang.org, so dtolnay/rust-toolchain
times out every build. The runner host has Rust installed and bind-mounts
~/.cargo into the container — use that directly and skip the download.
Also bump cinny submodule to 2178295e.

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

.gitea/workflows/release.yml

@@ -137,7 +137,16 @@ jobs:
             xdg-utils \
             squashfs-tools
 
-      - uses: dtolnay/rust-toolchain@stable
+      - name: Set up Rust toolchain
+        run: |
+          source "$HOME/.cargo/env" 2>/dev/null || true
+          if command -v cargo >/dev/null 2>&1; then
+            echo "Using existing Rust: $(cargo --version)"
+          else
+            curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --no-modify-path --default-toolchain stable --profile minimal
+            source "$HOME/.cargo/env"
+          fi
+          echo "$HOME/.cargo/bin" >> $GITHUB_PATH
 
       - uses: Swatinem/rust-cache@v2
         with: