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.

config/config.go

@@ -397,7 +397,7 @@ func preventClose(text string) {
 	fmt.Println("\nFailed to start Erupe:\n" + text)
 	go wait()
 	fmt.Println("\nPress Enter/Return to exit...")
-	fmt.Scanln()
+	_, _ = fmt.Scanln()
 	os.Exit(0)
 }
 

config/config_load_test.go

@@ -14,7 +14,7 @@ func TestLoadConfigNoFile(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Failed to get working directory: %v", err)
 	}
-	defer os.Chdir(oldWd)
+	defer func() { _ = os.Chdir(oldWd) }()
 
 	if err := os.Chdir(tmpDir); err != nil {
 		t.Fatalf("Failed to change directory: %v", err)
@@ -202,9 +202,6 @@ func TestConfigNilSafety(t *testing.T) {
 	}
 
 	cfg = &Config{}
-	if cfg == nil {
-		t.Error("Config should be allocated")
-	}
 
 	cfg.Host = "test"
 	if cfg.Host != "test" {