Fix golangci-lint v2 config: use linters.exclusions format

v2 moved issues.exclude-rules to linters.exclusions.rules and
issues.exclude-dirs to linters.exclusions.paths. Enable the
std-error-handling preset for defer Close() patterns.

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

.golangci.yml

@@ -8,26 +8,21 @@ linters:
     - ineffassign
     - staticcheck
     - unused
-
-issues:
-  exclude-dirs:
+  exclusions:
+    presets:
+      - std-error-handling
+    rules:
+      # binary.Write in ICO header encoding — panic-level errors only
+      - path: internal/icons/render\.go
+        linters: [errcheck]
+        source: "binary\\.Write"
+      # systray menu.ShowMenu has no meaningful error
+      - path: internal/tray/
+        linters: [errcheck]
+        source: "ShowMenu"
+      # Setup binary is a CLI wizard; best-effort error handling is acceptable
+      - path: cmd/setup/
+        linters: [errcheck, gosec]
+    paths:
       - cmd/panel
       - cmd/icongen
-  exclude-rules:
-    # defer body.Close() — safe pattern, return value is irrelevant
-    - linters: [errcheck]
-      source: "defer .+\\.Close\\(\\)"
-    # resp.Body.Close in non-defer context (checked via HTTP status already)
-    - linters: [errcheck]
-      source: "\\.Body\\.Close\\(\\)"
-    # systray menu.ShowMenu has no meaningful error
-    - linters: [errcheck]
-      path: internal/tray/
-      source: "ShowMenu"
-    # binary.Write in ICO header encoding — panic-level errors only
-    - linters: [errcheck]
-      path: internal/icons/render\.go
-      source: "binary\\.Write"
-    # Setup binary is a CLI wizard; best-effort error handling is acceptable
-    - linters: [errcheck, gosec]
-      path: cmd/setup/