Fix get_current_time tool

On ESP IDF 5.5 the get_current_time tool returns ESP_ERR_NOT_FOUND because
there is no "Date" header. This is because esp_http_client_get_header
only reads request headers. Response headers are only available via the
HTTP_EVENT_ON_HEADER event callback. They're dispatched and freed as they're
parsed.

Register an event handler that captures the "Date" header during HTTP response
parsing. The date string from this header is available as part of user context
after the HTTP request is finished.

main/tools/tool_get_time.c

@@ -106,33 +106,54 @@ static esp_err_t fetch_time_via_proxy(char *out, size_t out_size)
     return ESP_OK;
 }
 
+/* Event handler that captures the Date response header */
+typedef struct {
+    char date_val[64];
+} time_header_ctx_t;
+
+/**
+ * HTTP event handler that captures the "Date" response header.
+ *
+ * esp_http_client_get_header() only accesses request headers, so response
+ * headers must be captured here during HTTP_EVENT_ON_HEADER events.
+ * The Date value is copied into the time_header_ctx_t provided via user_data.
+ */
+static esp_err_t time_http_event_handler(esp_http_client_event_t *evt)
+{
+    time_header_ctx_t *ctx = evt->user_data;
+    if (evt->event_id == HTTP_EVENT_ON_HEADER) {
+        if (strcasecmp(evt->header_key, "Date") == 0 && ctx) {
+            strncpy(ctx->date_val, evt->header_value, sizeof(ctx->date_val) - 1);
+            ctx->date_val[sizeof(ctx->date_val) - 1] = '\0';
+        }
+    }
+    return ESP_OK;
+}
+
 /* Fetch time via direct HTTPS */
 static esp_err_t fetch_time_direct(char *out, size_t out_size)
 {
+    time_header_ctx_t ctx = {0};
+
     esp_http_client_config_t config = {
         .url = "https://api.telegram.org/",
         .method = HTTP_METHOD_HEAD,
         .timeout_ms = 10000,
         .crt_bundle_attach = esp_crt_bundle_attach,
+        .event_handler = time_http_event_handler,
+        .user_data = &ctx,
     };
 
     esp_http_client_handle_t client = esp_http_client_init(&config);
     if (!client) return ESP_FAIL;
 
     esp_err_t err = esp_http_client_perform(client);
-    if (err != ESP_OK) {
-        esp_http_client_cleanup(client);
-        return err;
-    }
-
-    /* Get Date header */
-    char *date_ptr = NULL;
-    esp_http_client_get_header(client, "Date", &date_ptr);
     esp_http_client_cleanup(client);
 
-    if (!date_ptr || date_ptr[0] == '\0') return ESP_ERR_NOT_FOUND;
+    if (err != ESP_OK) return err;
+    if (ctx.date_val[0] == '\0') return ESP_ERR_NOT_FOUND;
 
-    if (!parse_and_set_time(date_ptr, out, out_size)) return ESP_FAIL;
+    if (!parse_and_set_time(ctx.date_val, out, out_size)) return ESP_FAIL;
     return ESP_OK;
 }