feat: 添加时区设置功能，默认时区改为 CST-8

- 新增 set_timezone LLM 工具，支持通过对话设置时区
- 新增 set_timezone / timezone_show CLI 命令
- 默认时区从 PST 改为 CST-8（中国标准时间 UTC+8）
- 支持 POSIX 格式和 18 个城市名映射（Asia/Shanghai 等）
- 时区通过 NVS 持久化存储（system_config namespace）
- config_show 中显示当前时区配置
- 更新 changelog.md 和 taolun.md 文档

main/cli/serial_cli.c

@@ -17,6 +17,8 @@
 #include <string.h>
 #include <stdio.h>
 #include <ctype.h>
+#include <stdbool.h>
+#include <time.h>
 #include <dirent.h>
 #include "esp_log.h"
 #include "esp_console.h"
@@ -654,6 +656,11 @@ static int cmd_config_show(int argc, char **argv)
     print_config_u16("Proxy Port", MIMI_NVS_PROXY, MIMI_NVS_KEY_PROXY_PORT, MIMI_SECRET_PROXY_PORT);
     print_config("Search Key", MIMI_NVS_SEARCH, MIMI_NVS_KEY_API_KEY,  MIMI_SECRET_SEARCH_KEY, true);
     print_config("Tavily Key", MIMI_NVS_SEARCH, MIMI_NVS_KEY_TAVILY_KEY, MIMI_SECRET_TAVILY_KEY, true);
+    
+    /* System configs */
+    printf("  --- System configs ---\n");
+    print_config("Timezone", "system_config", MIMI_NVS_KEY_TIMEZONE, MIMI_TIMEZONE, false);
+    
     printf("=============================\n");
     return 0;
 }
@@ -676,6 +683,87 @@ static int cmd_config_reset(int argc, char **argv)
     return 0;
 }
 
+/* --- set_timezone command --- */
+static struct {
+    struct arg_str *tz;
+    struct arg_end *end;
+} timezone_args;
+
+static int cmd_set_timezone(int argc, char **argv)
+{
+    int nerrors = arg_parse(argc, argv, (void **)&timezone_args);
+    if (nerrors != 0) {
+        arg_print_errors(stderr, timezone_args.end, argv[0]);
+        return 1;
+    }
+
+    const char *tz_str = timezone_args.tz->sval[0];
+    nvs_handle_t nvs;
+    esp_err_t err = nvs_open("system_config", NVS_READWRITE, &nvs);
+    if (err != ESP_OK) {
+        printf("Failed to open NVS: %s\n", esp_err_to_name(err));
+        return 1;
+    }
+
+    err = nvs_set_str(nvs, MIMI_NVS_KEY_TIMEZONE, tz_str);
+    if (err != ESP_OK) {
+        printf("Failed to save timezone: %s\n", esp_err_to_name(err));
+        nvs_close(nvs);
+        return 1;
+    }
+
+    err = nvs_commit(nvs);
+    nvs_close(nvs);
+
+    if (err != ESP_OK) {
+        printf("Failed to commit NVS: %s\n", esp_err_to_name(err));
+        return 1;
+    }
+
+    setenv("TZ", tz_str, 1);
+    tzset();
+
+    time_t now = time(NULL);
+    struct tm tm_now;
+    localtime_r(&now, &tm_now);
+    char time_str[64];
+    strftime(time_str, sizeof(time_str), "%Y-%m-%d %H:%M:%S %Z", &tm_now);
+
+    printf("Timezone set to '%s'. Current time: %s. Restart to apply permanently.\n", tz_str, time_str);
+    return 0;
+}
+
+/* --- timezone_show command --- */
+static int cmd_timezone_show(int argc, char **argv)
+{
+    (void)argc;
+    (void)argv;
+
+    char nvs_val[64] = {0};
+    const char *source = "build";
+    const char *display = MIMI_TIMEZONE;
+
+    nvs_handle_t nvs;
+    if (nvs_open("system_config", NVS_READONLY, &nvs) == ESP_OK) {
+        size_t len = sizeof(nvs_val);
+        if (nvs_get_str(nvs, MIMI_NVS_KEY_TIMEZONE, nvs_val, &len) == ESP_OK && nvs_val[0]) {
+            source = "NVS";
+            display = nvs_val;
+        }
+        nvs_close(nvs);
+    }
+
+    printf("Current timezone: %s [%s]\n", display, source);
+
+    time_t now = time(NULL);
+    struct tm tm_now;
+    localtime_r(&now, &tm_now);
+    char time_str[64];
+    strftime(time_str, sizeof(time_str), "%Y-%m-%d %H:%M:%S %Z (%A)", &tm_now);
+    printf("Local time: %s\n", time_str);
+    return 0;
+}
+
 /* --- heartbeat_trigger command --- */
 static int cmd_heartbeat_trigger(int argc, char **argv)
 {
@@ -736,13 +824,22 @@ typedef struct {
     size_t output_size;
     esp_err_t err;
     SemaphoreHandle_t done;
+    bool timed_out;
 } web_search_task_ctx_t;
 
 static void web_search_task(void *arg)
 {
     web_search_task_ctx_t *task_ctx = (web_search_task_ctx_t *)arg;
     task_ctx->err = tool_web_search_execute(task_ctx->input_json, task_ctx->output, task_ctx->output_size);
-    xSemaphoreGive(task_ctx->done);
+    if (!task_ctx->timed_out) {
+        xSemaphoreGive(task_ctx->done);
+    } else {
+        /* Main thread timed out and freed ctx, so we must clean up ourselves */
+        free((void *)task_ctx->input_json);
+        free(task_ctx->output);
+        vSemaphoreDelete(task_ctx->done);
+        free(task_ctx);
+    }
     vTaskDelete(NULL);
 }
 
@@ -838,10 +935,8 @@ static int cmd_web_search(int argc, char **argv)
 
     if (xSemaphoreTake(ctx->done, pdMS_TO_TICKS(45000)) != pdTRUE) {
         printf("web_search status: timeout\n");
-        vSemaphoreDelete(ctx->done);
-        free(input_copy);
-        free(ctx);
-        free(output);
+        ctx->timed_out = true;
+        /* Task will clean up ctx, input_copy, output, and done on its own */
         return 1;
     }
     esp_err_t err = ctx->err;
@@ -1163,6 +1258,25 @@ esp_err_t serial_cli_init(void)
     };
     esp_console_cmd_register(&config_reset_cmd);
 
+    /* set_timezone */
+    timezone_args.tz = arg_str1(NULL, NULL, "<timezone>", "Timezone (e.g. CST-8, Asia/Shanghai)");
+    timezone_args.end = arg_end(1);
+    esp_console_cmd_t set_timezone_cmd = {
+        .command = "set_timezone",
+        .help = "Set system timezone (e.g. set_timezone CST-8)",
+        .func = &cmd_set_timezone,
+        .argtable = &timezone_args,
+    };
+    esp_console_cmd_register(&set_timezone_cmd);
+
+    /* timezone_show */
+    esp_console_cmd_t timezone_show_cmd = {
+        .command = "timezone_show",
+        .help = "Show current timezone and local time",
+        .func = &cmd_timezone_show,
+    };
+    esp_console_cmd_register(&timezone_show_cmd);
+
     /* heartbeat_trigger */
     esp_console_cmd_t heartbeat_cmd = {
         .command = "heartbeat_trigger",