fix(ci): install sccache with S3 feature if missing

The distro sccache package lacks S3 support. Install from cargo
with --features s3 if the existing binary can't connect to the
S3 backend. Skips install if already present and working.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -23,6 +23,14 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
+      - name: Ensure sccache with S3 support
+        run: |
+          if sccache --version 2>/dev/null && sccache --show-stats 2>/dev/null; then
+            echo "sccache with S3 support already installed"
+          else
+            cargo install sccache --features s3 --locked
+          fi
+
       - name: Check formatting
         run: cargo fmt --check --all