fix CI: use pre-built golangci-lint binary and install sqlite3

Two issues caused CI failures:

1. golangci-lint v2.10.1 requires Go >= 1.25.0, but the project uses
   Go 1.24.4 (from go.mod). The previous `go install` approach tried
   to compile golangci-lint from source, which fails due to the Go
   version mismatch. Fix: download the pre-built binary via the
   official install script, pinned to the same commit SHA (5d1e709)
   for security.

2. TestBackupAndRestore fails because vacuumDatabase() shells out to
   the `sqlite3` CLI binary, which is not installed in the CI runner
   image. Fix: install sqlite3 via apt-get in CI.

.gitea/workflows/check.yml

@@ -12,7 +12,11 @@ jobs:
       - uses: actions/setup-go@40f1582b2485089dde7abd97c1529aa768e1baff # v5
         with:
           go-version-file: go.mod
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update -qq
+          sudo apt-get install -y -qq sqlite3
       - name: Install golangci-lint
-        run: go install github.com/golangci/golangci-lint/v2/cmd/golangci-lint@5d1e709b7be35cb2025444e19de266b056b7b7ee # v2.10.1
+        run: curl -sSfL https://raw.githubusercontent.com/golangci/golangci-lint/5d1e709b7be35cb2025444e19de266b056b7b7ee/install.sh | sh -s -- -b "$(go env GOPATH)/bin" v2.10.1
       - name: Run checks
         run: make check