feat: 添加编译时模块开关配置

通过 sdkconfig.defaults 选择性启用/禁用模块，减少固件体积：

新增模块开关：
- CONFIG_MIMI_CHAN_TELEGRAM (默认 n)
- CONFIG_MIMI_CHAN_FEISHU (默认 y)
- CONFIG_MIMI_TOOL_WEB_SEARCH (默认 y)
- CONFIG_MIMI_TOOL_GPIO (默认 n)
- CONFIG_MIMI_WS_SERVER (默认 y)
- CONFIG_MIMI_WIFI_ONBOARD (默认 y)
- CONFIG_MIMI_OTA (默认 n)

技术实现：
- CMakeLists.txt 条件编译源文件
- 头文件使用 static inline stub
- CLI 命令和工具注册也支持条件编译

消除 Telegram 未配置时的 5 秒轮询警告日志

main/onboard/wifi_onboard.h

@@ -2,14 +2,21 @@
 
 #include "esp_err.h"
 
+#ifdef CONFIG_MIMI_WIFI_ONBOARD
 typedef enum {
     WIFI_ONBOARD_MODE_CAPTIVE = 0,
     WIFI_ONBOARD_MODE_ADMIN,
 } wifi_onboard_mode_t;
 
-/**
- * Start WiFi onboarding/configuration portal.
- * CAPTIVE mode opens DNS hijack + config page and blocks forever.
- * ADMIN mode keeps a local config hotspot alive without captive redirects.
- */
 esp_err_t wifi_onboard_start(wifi_onboard_mode_t mode);
+#else
+typedef enum {
+    WIFI_ONBOARD_MODE_CAPTIVE = 0,
+    WIFI_ONBOARD_MODE_ADMIN,
+} wifi_onboard_mode_t;
+
+static inline esp_err_t wifi_onboard_start(wifi_onboard_mode_t mode) {
+    (void)mode;
+    return ESP_OK;
+}
+#endif