fix: re-enable CI lint job and fix ~65 lint errors (partial)

Re-enable the golangci-lint job in CI (disabled Oct 2025), update to
Go 1.25 and golangci-lint-action v7. Fix errcheck, gosimple S1009,
staticcheck SA4031 and SA2001 errors across 54 files. Remaining ~39
lint errors will be addressed in follow-up commits.

.github/workflows/go-improved.yml

@@ -104,23 +104,20 @@ jobs:
           ./bundled-schema/
         retention-days: 7
 
-  # lint:
-  #   name: Lint
-  #   runs-on: ubuntu-latest
-  #
-  #   steps:
-  #   - uses: actions/checkout@v4
-  #
-  #   - name: Set up Go
-  #     uses: actions/setup-go@v5
-  #     with:
-  #       go-version: '1.23'
-  #
-  #   - name: Run golangci-lint
-  #     uses: golangci/golangci-lint-action@v3
-  #     with:
-  #       version: latest
-  #       args: --timeout=5m --out-format=github-actions
-  #
-  # TEMPORARILY DISABLED: Linting check deactivated to allow ongoing linting fixes
-  # Re-enable after completing all linting issues
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Go
+      uses: actions/setup-go@v5
+      with:
+        go-version: '1.25'
+
+    - name: Run golangci-lint
+      uses: golangci/golangci-lint-action@v7
+      with:
+        version: latest
+        args: --timeout=5m --out-format=github-actions