fix: update JSON fields from snake_case to camelCase and make tests quiet by default

- Update all JSON field references in tests from snake_case to camelCase
- Update vault list JSON output to use currentVault instead of current_vault
- Make integration tests quiet by default unless run with -v flag
- Fix tests that were using exec.Command to use in-process execution helpers
- Tests now only show debug output when explicitly requested or on failure

internal/cli/vault.go

@@ -108,8 +108,8 @@ func (cli *Instance) ListVaults(cmd *cobra.Command, jsonOutput bool) error {
 		}
 
 		result := map[string]interface{}{
-			"vaults":        vaults,
-			"current_vault": currentVault,
+			"vaults":       vaults,
+			"currentVault": currentVault,
 		}
 
 		jsonBytes, err := json.MarshalIndent(result, "", "  ")