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/tools/gpio_policy.c

@@ -4,6 +4,7 @@
 
 #include <stdlib.h>
 #include <stdio.h>
+#include <stdbool.h>
 #include <string.h>
 
 #ifndef GPIO_IS_VALID_GPIO

main/tools/tool_get_time.c

@@ -4,6 +4,7 @@
 
 #include <string.h>
 #include <stdlib.h>
+#include <stdbool.h>
 #include <time.h>
 #include <sys/time.h>
 #include "esp_log.h"

main/tools/tool_registry.c

@@ -2,6 +2,7 @@
 #include "mimi_config.h"
 #include "tools/tool_web_search.h"
 #include "tools/tool_get_time.h"
+#include "tools/tool_set_timezone.h"
 #include "tools/tool_files.h"
 #include "tools/tool_cron.h"
 #include "tools/tool_gpio.h"
@@ -83,6 +84,18 @@ esp_err_t tool_registry_init(void)
     };
     register_tool(&gt);
 
+    /* Register set_timezone */
+    mimi_tool_t stz = {
+        .name = "set_timezone",
+        .description = "Set the system timezone. Accepts POSIX format (e.g. CST-8, EST5EDT,M3.2.0,M11.1.0) or city name (e.g. Asia/Shanghai, America/New_York).",
+        .input_schema_json =
+            "{\"type\":\"object\","
+            "\"properties\":{\"timezone\":{\"type\":\"string\",\"description\":\"Timezone in POSIX format or city name (e.g. CST-8, Asia/Shanghai)\"}},"
+            "\"required\":[\"timezone\"]}",
+        .execute = tool_set_timezone_execute,
+    };
+    register_tool(&stz);
+
     /* Register read_file */
     mimi_tool_t rf = {
         .name = "read_file",

main/tools/tool_set_timezone.c

@@ -0,0 +1,145 @@
+#include "tool_set_timezone.h"
+#include "mimi_config.h"
+
+#include <string.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <time.h>
+#include "esp_log.h"
+#include "nvs.h"
+#include "cJSON.h"
+
+static const char *TAG = "tool_timezone";
+
+/* Common timezone mappings for user-friendly names */
+typedef struct {
+    const char *name;
+    const char *posix_tz;
+} tz_mapping_t;
+
+static const tz_mapping_t tz_mappings[] = {
+    { "Asia/Shanghai", "CST-8" },
+    { "Asia/Beijing", "CST-8" },
+    { "Asia/Hong_Kong", "HKT-8" },
+    { "Asia/Tokyo", "JST-9" },
+    { "Asia/Seoul", "KST-9" },
+    { "Asia/Singapore", "SGT-8" },
+    { "Asia/Kolkata", "IST-5:30" },
+    { "Asia/Dubai", "GST-4" },
+    { "Europe/London", "GMT0BST,M3.5.0/1,M10.5.0" },
+    { "Europe/Paris", "CET-1CEST,M3.5.0,M10.5.0/3" },
+    { "Europe/Berlin", "CET-1CEST,M3.5.0,M10.5.0/3" },
+    { "America/New_York", "EST5EDT,M3.2.0,M11.1.0" },
+    { "America/Chicago", "CST6CDT,M3.2.0,M11.1.0" },
+    { "America/Denver", "MST7MDT,M3.2.0,M11.1.0" },
+    { "America/Los_Angeles", "PST8PDT,M3.2.0,M11.1.0" },
+    { "Australia/Sydney", "AEST-10AEDT,M10.1.0,M4.1.0/3" },
+    { "UTC", "UTC0" },
+    { "GMT", "GMT0" },
+};
+
+static const char *resolve_timezone(const char *tz_str)
+{
+    if (!tz_str || !tz_str[0]) return NULL;
+
+    for (size_t i = 0; i < sizeof(tz_mappings) / sizeof(tz_mappings[0]); i++) {
+        if (strcmp(tz_str, tz_mappings[i].name) == 0) {
+            return tz_mappings[i].posix_tz;
+        }
+    }
+
+    return tz_str;
+}
+
+static bool validate_timezone(const char *tz_str)
+{
+    if (!tz_str || !tz_str[0]) return false;
+    if (strlen(tz_str) > 64) return false;
+
+    for (size_t i = 0; i < sizeof(tz_mappings) / sizeof(tz_mappings[0]); i++) {
+        if (strcmp(tz_str, tz_mappings[i].name) == 0) return true;
+    }
+
+    if (strchr(tz_str, '+') || strchr(tz_str, '-') ||
+        strcmp(tz_str, "UTC0") == 0 || strcmp(tz_str, "GMT0") == 0) {
+        return true;
+    }
+
+    return false;
+}
+
+static esp_err_t save_timezone_nvs(const char *tz_str)
+{
+    nvs_handle_t nvs;
+    esp_err_t err = nvs_open("system_config", NVS_READWRITE, &nvs);
+    if (err != ESP_OK) {
+        ESP_LOGE(TAG, "Failed to open NVS: %s", esp_err_to_name(err));
+        return err;
+    }
+
+    err = nvs_set_str(nvs, MIMI_NVS_KEY_TIMEZONE, tz_str);
+    if (err != ESP_OK) {
+        ESP_LOGE(TAG, "Failed to save timezone: %s", esp_err_to_name(err));
+        nvs_close(nvs);
+        return err;
+    }
+
+    err = nvs_commit(nvs);
+    nvs_close(nvs);
+
+    if (err != ESP_OK) {
+        ESP_LOGE(TAG, "Failed to commit NVS: %s", esp_err_to_name(err));
+        return err;
+    }
+
+    return ESP_OK;
+}
+
+esp_err_t tool_set_timezone_execute(const char *input_json, char *output, size_t output_size)
+{
+    ESP_LOGI(TAG, "Setting timezone...");
+
+    cJSON *root = cJSON_Parse(input_json);
+    if (!root) {
+        snprintf(output, output_size, "Error: invalid JSON input");
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    cJSON *tz_item = cJSON_GetObjectItem(root, "timezone");
+    if (!tz_item || !cJSON_IsString(tz_item)) {
+        cJSON_Delete(root);
+        snprintf(output, output_size, "Error: 'timezone' field required (string)");
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    const char *input_tz = tz_item->valuestring;
+    const char *resolved_tz = resolve_timezone(input_tz);
+
+    if (!resolved_tz || !validate_timezone(resolved_tz)) {
+        cJSON_Delete(root);
+        snprintf(output, output_size, "Error: invalid timezone format '%s'. Use POSIX format (e.g. CST-8) or city name (e.g. Asia/Shanghai)", input_tz);
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    esp_err_t err = save_timezone_nvs(resolved_tz);
+    if (err != ESP_OK) {
+        cJSON_Delete(root);
+        snprintf(output, output_size, "Error: failed to save timezone (%s)", esp_err_to_name(err));
+        return err;
+    }
+
+    setenv("TZ", resolved_tz, 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);
+
+    cJSON_Delete(root);
+    snprintf(output, output_size, "Timezone set to '%s'. Current time: %s", resolved_tz, time_str);
+    ESP_LOGI(TAG, "Timezone set to: %s, current time: %s", resolved_tz, time_str);
+
+    return ESP_OK;
+}

main/tools/tool_set_timezone.h

@@ -0,0 +1,11 @@
+#pragma once
+
+#include "esp_err.h"
+#include <stddef.h>
+
+/**
+ * Execute set_timezone tool.
+ * Sets the system timezone via NVS and updates the TZ environment variable.
+ * Input JSON: {"timezone": "CST-8"} or {"timezone": "Asia/Shanghai"}
+ */
+esp_err_t tool_set_timezone_execute(const char *input_json, char *output, size_t output_size);