fix(ci): use Gitea-native checkout action

The GitHub actions/checkout@v4 requires Node.js which is not
available in the rust container image. Switch to Gitea's native
checkout action that runs without Node.js.

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

.gitea/workflows/ci.yml

@@ -27,7 +27,7 @@ jobs:
     container:
       image: rust:1.89-bookworm
     steps:
-      - uses: actions/checkout@v4
+      - uses: https://gitea.com/https://gitea.com/actions/checkout@v4
       - run: rustup component add rustfmt
       - run: cargo fmt --check
 
@@ -37,7 +37,7 @@ jobs:
     container:
       image: rust:1.89-bookworm
     steps:
-      - uses: actions/checkout@v4
+      - uses: https://gitea.com/https://gitea.com/actions/checkout@v4
       - run: rustup component add clippy
       # Lint both feature sets independently
       - name: Clippy (server)
@@ -51,7 +51,7 @@ jobs:
     container:
       image: rust:1.89-bookworm
     steps:
-      - uses: actions/checkout@v4
+      - uses: https://gitea.com/actions/checkout@v4
       - run: cargo install cargo-audit
       - run: cargo audit
 
@@ -65,7 +65,7 @@ jobs:
     container:
       image: rust:1.89-bookworm
     steps:
-      - uses: actions/checkout@v4
+      - uses: https://gitea.com/actions/checkout@v4
       - name: Run tests (server)
         run: cargo test --features server --no-default-features
       - name: Run tests (web)
@@ -83,7 +83,7 @@ jobs:
       github.event_name == 'push' &&
       (github.ref == 'refs/heads/main' || startsWith(github.ref, 'refs/heads/release/'))
     steps:
-      - uses: actions/checkout@v4
+      - uses: https://gitea.com/actions/checkout@v4
 
       - name: Determine image tag
         id: tag