fix(ci): resolve Windows Cargo SSL handshake failures on crates.io

Three changes to the build-windows job:

1. CARGO_REGISTRIES_CRATES_IO_PROTOCOL=sparse — uses lightweight HTTPS
   per-crate fetching instead of a full git clone of the crates.io index.
   The git clone path triggers an SSL connection reset ([curl 35]) on
   Windows Schannel in this runner environment.

2. CARGO_HTTP_MULTIPLEXING=false — disables HTTP/2 ALPN negotiation which
   is another common source of Schannel SSL resets on Windows.

3. CARGO_NET_RETRY=5 — retry transient network errors up to 5 times before
   failing the build.

4. Add Swatinem/rust-cache for Windows (mirrors the Linux job) — after a
   successful build, compiled crates are cached so subsequent runs skip the
   crates.io download entirely.

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

.gitea/workflows/release.yml

@@ -63,6 +63,10 @@ jobs:
           $ver = '${{ needs.prepare.outputs.version }}'
           node -e "const fs=require('fs');const d=JSON.parse(fs.readFileSync('src-tauri/tauri.conf.json','utf8'));d.version='$ver';fs.writeFileSync('src-tauri/tauri.conf.json',JSON.stringify(d,null,2),'utf8');"
 
+      - uses: Swatinem/rust-cache@v2
+        with:
+          workspaces: src-tauri
+
       - name: Install frontend deps
         shell: powershell
         run: cd cinny; npm ci
@@ -77,6 +81,13 @@ jobs:
           TAURI_SIGNING_PRIVATE_KEY: ${{ secrets.TAURI_SIGNING_PRIVATE_KEY }}
           TAURI_SIGNING_PRIVATE_KEY_PASSWORD: ''
           NODE_OPTIONS: '--max_old_space_size=4096'
+          # Sparse registry avoids a full git clone of the crates.io index —
+          # eliminates the curl SSL handshake failures seen on Windows runners.
+          CARGO_REGISTRIES_CRATES_IO_PROTOCOL: sparse
+          # Disable HTTP/2 multiplexing — ALPN negotiation can reset on Windows Schannel.
+          CARGO_HTTP_MULTIPLEXING: 'false'
+          # Retry transient network errors before failing.
+          CARGO_NET_RETRY: '5'
         run: npm run tauri -- build --bundles nsis
 
       - name: Upload to release