feat(cli): migrate console calls to debugLogger and stdioHelpers (M3 Phase 7-9)

Route CLI console.* calls to structured logging:
- Debug/internal diagnostics → debugLogger (logfile)
- User-facing output → writeStdoutLine/writeStderrLine/clearScreen (stdioHelpers)
- Add stdioHelpers.ts with writeStdoutLine, writeStderrLine, clearScreen
- Migrate pre-session files (gemini.tsx, sandbox.ts, config.ts) to stdioHelpers
- Migrate extension/MCP commands to stdioHelpers
- Migrate non-interactive session/control to debugLogger
- Migrate UI hooks and components to debugLogger

packages/cli/src/utils/stdioHelpers.ts

@@ -0,0 +1,41 @@
+/**
+ * @license
+ * Copyright 2025 Qwen Team
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/**
+ * Utility functions for writing to stdout/stderr in CLI commands.
+ *
+ * These helpers are used instead of console.log/console.error in standalone
+ * CLI commands (like `qwen extensions list`) where the output IS the user-facing
+ * result, not debug logging.
+ *
+ * For debug/diagnostic logging, use `createDebugLogger()` from @qwen-code/qwen-code-core.
+ */
+
+/**
+ * Writes a message to stdout with a trailing newline.
+ * Use for normal command output that the user expects to see.
+ * Avoids double newlines if the message already ends with one.
+ */
+export const writeStdoutLine = (message: string): void => {
+  process.stdout.write(message.endsWith('\n') ? message : `${message}\n`);
+};
+
+/**
+ * Writes a message to stderr with a trailing newline.
+ * Use for error messages in CLI commands.
+ * Avoids double newlines if the message already ends with one.
+ */
+export const writeStderrLine = (message: string): void => {
+  process.stderr.write(message.endsWith('\n') ? message : `${message}\n`);
+};
+
+/**
+ * Clears the terminal screen.
+ * Use instead of console.clear() to satisfy no-console lint rules.
+ */
+export const clearScreen = (): void => {
+  console.clear();
+};