Gitea runners do not have Node.js installed, which is required
for all JavaScript-based GitHub Actions including actions/checkout.
- Replace all actions/checkout@v4 with manual git fetch/checkout
- All checkout logic now uses shell commands only
- No JavaScript-based actions remain in the workflow
- Remove dtolnay/rust-toolchain (JS action) → use rustup via curl
- Remove Swatinem/rust-cache (JS action) → no replacement, builds from scratch
- All jobs now install Rust toolchain via shell commands
- Alpine job installs rustup directly with musl target support
- Ensures compatibility with Gitea Actions runners
