fix(ci): reduce disk usage — skip host cargo build, test only

os error 5 (I/O error) = disk full. Two full Rust compiles
(host cargo build + Docker cargo build) exceed runner disk.
Keep only cargo test --lib on host, full build inside Docker.

.gitea/workflows/build.yaml

@@ -35,11 +35,9 @@ jobs:
       - name: Checkout code
         uses: actions/checkout@v4
 
-      - name: Cargo build, test, clippy (single compile pass)
+      - name: Cargo test (lib only, no full build)
         run: |
-          cargo build --all --verbose
           cargo test --all --lib --verbose 2>&1 | tail -150 || true
-          cargo clippy --all --all-targets -- -D warnings 2>&1 | tail -50 || true
 
       - name: Get short SHA
         id: sha
@@ -60,7 +58,8 @@ jobs:
       - name: Clean cargo before Docker build
         run: |
           cargo clean || true
-          rm -rf ~/.cargo/registry/cache ~/.cargo/registry/index ~/.cargo/git || true
+          rm -rf target/ || true
+          rm -rf ~/.cargo/registry/cache || true
           df -h /
 
       - name: Build and push Docker image (SHA tag only)