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/gateway/ws_server.h

@@ -2,24 +2,15 @@
 
 #include "esp_err.h"
 
-/**
- * Initialize and start the WebSocket server on MIMI_WS_PORT.
- * Allows external clients to interact with the Agent via JSON messages.
- *
- * Protocol:
- *   Inbound:  {"type":"message","content":"hello","chat_id":"ws_client1"}
- *   Outbound: {"type":"response","content":"Hi!","chat_id":"ws_client1"}
- */
+#ifdef CONFIG_MIMI_WS_SERVER
 esp_err_t ws_server_start(void);
-
-/**
- * Send a text message to a specific WebSocket client by chat_id.
- * @param chat_id  Client identifier (assigned on connection)
- * @param text     Message text
- */
 esp_err_t ws_server_send(const char *chat_id, const char *text);
-
-/**
- * Stop the WebSocket server.
- */
 esp_err_t ws_server_stop(void);
+#else
+static inline esp_err_t ws_server_start(void) { return ESP_OK; }
+static inline esp_err_t ws_server_send(const char *chat_id, const char *text) {
+    (void)chat_id; (void)text;
+    return ESP_OK;
+}
+static inline esp_err_t ws_server_stop(void) { return ESP_OK; }
+#endif