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/tools/tool_web_search.h

@@ -2,28 +2,28 @@
 
 #include "esp_err.h"
 #include <stddef.h>
+#include <stdio.h>
 
-/**
- * Initialize web search tool.
- */
+#ifdef CONFIG_MIMI_TOOL_WEB_SEARCH
 esp_err_t tool_web_search_init(void);
-
-/**
- * Execute a web search.
- *
- * @param input_json   JSON string with "query" field
- * @param output       Output buffer for formatted search results
- * @param output_size  Size of output buffer
- * @return ESP_OK on success
- */
 esp_err_t tool_web_search_execute(const char *input_json, char *output, size_t output_size);
-
-/**
- * Save Brave Search API key to NVS.
- */
 esp_err_t tool_web_search_set_key(const char *api_key);
-
-/**
- * Save Tavily API key to NVS.
- */
 esp_err_t tool_web_search_set_tavily_key(const char *api_key);
+#else
+static inline esp_err_t tool_web_search_init(void) { return ESP_OK; }
+static inline esp_err_t tool_web_search_execute(const char *input_json, char *output, size_t output_size) {
+    (void)input_json; (void)output; (void)output_size;
+    if (output && output_size > 0) {
+        snprintf(output, output_size, "Error: Web search tool is disabled in this build.");
+    }
+    return ESP_OK;
+}
+static inline esp_err_t tool_web_search_set_key(const char *api_key) {
+    (void)api_key;
+    return ESP_OK;
+}
+static inline esp_err_t tool_web_search_set_tavily_key(const char *api_key) {
+    (void)api_key;
+    return ESP_OK;
+}
+#endif