test(docker): cover docker subcommand rendering paths

- add handler-level coverage for up, down, logs, config, update, and status

- exercise success, validation, follow-mode, and boxed error output paths

tests/unit/commands/docker-subcommand-test-helpers.ts

@@ -0,0 +1,44 @@
+import { afterEach, beforeEach, mock } from 'bun:test';
+
+export function useDockerSubcommandConsoleCapture(): {
+  logLines: string[];
+  errorLines: string[];
+} {
+  const state = {
+    logLines: [] as string[],
+    errorLines: [] as string[],
+  };
+
+  let originalConsoleLog: typeof console.log;
+  let originalConsoleError: typeof console.error;
+  let originalExitCode: number | undefined;
+
+  beforeEach(() => {
+    state.logLines = [];
+    state.errorLines = [];
+    originalConsoleLog = console.log;
+    originalConsoleError = console.error;
+    originalExitCode = process.exitCode;
+    process.exitCode = 0;
+
+    console.log = (...args: unknown[]) => {
+      state.logLines.push(args.map(String).join(' '));
+    };
+    console.error = (...args: unknown[]) => {
+      state.errorLines.push(args.map(String).join(' '));
+    };
+  });
+
+  afterEach(() => {
+    console.log = originalConsoleLog;
+    console.error = originalConsoleError;
+    process.exitCode = originalExitCode ?? 0;
+    mock.restore();
+  });
+
+  return state;
+}
+
+export function renderCapturedLines(lines: string[]): string {
+  return lines.join('\n');
+}