feat: add working indicator and get_current_time to system prompt

Send "mimi😗is working..." to user when processing starts.
List get_current_time in system prompt available tools so the agent
knows to call it for time/date queries. Remove auto time fetch from
system prompt builder — agent calls the tool on demand.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

main/agent/context_builder.c

@@ -4,7 +4,6 @@
 
 #include <stdio.h>
 #include <string.h>
-#include <time.h>
 #include "esp_log.h"
 #include "cJSON.h"
 
@@ -30,26 +29,18 @@ esp_err_t context_build_system_prompt(char *buf, size_t size)
 {
     size_t off = 0;
 
-    /* Identity header */
-    time_t now;
-    time(&now);
-    struct tm tm;
-    localtime_r(&now, &tm);
-    char time_str[64];
-    strftime(time_str, sizeof(time_str), "%Y-%m-%d %H:%M (%A)", &tm);
-
     off += snprintf(buf + off, size - off,
         "# MimiClaw\n\n"
         "You are MimiClaw, a personal AI assistant running on an ESP32-S3 device.\n"
         "You communicate through Telegram and WebSocket.\n\n"
-        "## Current Time\n%s\n\n"
         "Be helpful, accurate, and concise.\n\n"
         "## Available Tools\n"
         "You have access to the following tools:\n"
         "- web_search: Search the web for current information. "
-        "Use this when you need up-to-date facts, news, weather, or anything beyond your training data.\n\n"
-        "Use tools when needed. Provide your final answer as text after using tools.\n",
-        time_str);
+        "Use this when you need up-to-date facts, news, weather, or anything beyond your training data.\n"
+        "- get_current_time: Get the current date and time. "
+        "You do NOT have an internal clock — always use this tool when you need to know the time or date.\n\n"
+        "Use tools when needed. Provide your final answer as text after using tools.\n");
 
     /* Bootstrap files */
     off = append_file(buf, size, off, MIMI_SOUL_FILE, "Personality");