Fix WiFi reconnect bugs, negative-temp rounding, and stale docs

- Clear WIFI_CONNECTED_BIT on disconnect so wifi_is_connected() stops
  reporting a link that is gone; the weather task's reconnect path was
  dead code without it.
- After the 8 fast retries are spent, retry every 30s via an esp_timer
  forever instead of giving up until power cycle. FAIL_BIT now only
  unblocks the boot-time wait and is cleared on reconnect.
- Start the weather task even when the boot-time connect times out --
  the background retries may still bring WiFi up later. Only an empty
  SSID skips it.
- Round temperatures with lroundf(): the old +0.5f-and-truncate rounded
  toward zero below 0degF (-10.6 displayed as -10).
- Drop the stale single-framebuffer "Partial-mode flush" comment in
  display_rgb.c, fix the README paragraph claiming the bounce buffer is
  disabled (it is enabled and load-bearing), and correct the
  sdkconfig.defaults header to N16R8/16MB.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

main/wifi/wifi_manager.c

@@ -4,6 +4,7 @@
 #include "esp_log.h"
 #include "esp_netif.h"
 #include "esp_system.h"
+#include "esp_timer.h"
 #include "esp_wifi.h"
 #include "freertos/FreeRTOS.h"
 #include "freertos/event_groups.h"
@@ -18,10 +19,20 @@ static const char *TAG = "wifi_manager";
 #define WIFI_FAIL_BIT      BIT1
 #define WIFI_MAX_RETRIES   8
 #define WIFI_CONNECT_TIMEOUT_MS 30000
+/* After the fast retries are spent, keep trying at this interval forever --
+ * this is a wall appliance, so an AP outage must not require a power cycle. */
+#define WIFI_RECONNECT_DELAY_MS 30000
 
 static EventGroupHandle_t s_wifi_event_group = NULL;
+static esp_timer_handle_t s_reconnect_timer = NULL;
 static int s_retry_count = 0;
 
+static void reconnect_timer_cb(void *arg)
+{
+    ESP_LOGI(TAG, "Slow reconnect attempt");
+    esp_wifi_connect();
+}
+
 static void wifi_event_handler(void *arg, esp_event_base_t event_base,
                                int32_t event_id, void *event_data)
 {
@@ -31,18 +42,28 @@ static void wifi_event_handler(void *arg, esp_event_base_t event_base,
     }
 
     if (event_base == WIFI_EVENT && event_id == WIFI_EVENT_STA_DISCONNECTED) {
+        /* Without this, wifi_is_connected() keeps reporting true after a
+         * drop and callers never notice the link is gone. */
+        xEventGroupClearBits(s_wifi_event_group, WIFI_CONNECTED_BIT);
+
         /*
-         * Only give up after a bounded number of retries. Signalling failure
-         * on the first disconnect (as this previously did) meant a single
-         * transient drop was reported as a hard failure.
+         * A bounded burst of immediate retries covers transient drops;
+         * signalling failure on the first disconnect (as this previously did)
+         * meant a single blip was reported as a hard failure. Once the burst
+         * is spent, fall back to a slow periodic retry instead of giving up:
+         * FAIL_BIT only unblocks the boot-time wait in wifi_init_sta().
          */
         if (s_retry_count < WIFI_MAX_RETRIES) {
             s_retry_count++;
             ESP_LOGW(TAG, "Disconnected, retry %d/%d", s_retry_count, WIFI_MAX_RETRIES);
             esp_wifi_connect();
         } else {
-            ESP_LOGE(TAG, "Giving up after %d retries", WIFI_MAX_RETRIES);
+            ESP_LOGW(TAG, "Still down after %d fast retries; retrying every %d s",
+                     WIFI_MAX_RETRIES, WIFI_RECONNECT_DELAY_MS / 1000);
             xEventGroupSetBits(s_wifi_event_group, WIFI_FAIL_BIT);
+            esp_timer_stop(s_reconnect_timer);
+            esp_timer_start_once(s_reconnect_timer,
+                                 (uint64_t)WIFI_RECONNECT_DELAY_MS * 1000);
         }
         return;
     }
@@ -51,6 +72,7 @@ static void wifi_event_handler(void *arg, esp_event_base_t event_base,
         const ip_event_got_ip_t *event = (const ip_event_got_ip_t *)event_data;
         ESP_LOGI(TAG, "Got IP: " IPSTR, IP2STR(&event->ip_info.ip));
         s_retry_count = 0;
+        xEventGroupClearBits(s_wifi_event_group, WIFI_FAIL_BIT);
         xEventGroupSetBits(s_wifi_event_group, WIFI_CONNECTED_BIT);
     }
 }
@@ -67,6 +89,12 @@ esp_err_t wifi_init_sta(void)
         return ESP_ERR_NO_MEM;
     }
 
+    const esp_timer_create_args_t timer_args = {
+        .callback = reconnect_timer_cb,
+        .name = "wifi_reconnect",
+    };
+    ESP_ERROR_CHECK(esp_timer_create(&timer_args, &s_reconnect_timer));
+
     esp_err_t ret = nvs_flash_init();
     if (ret == ESP_ERR_NVS_NO_FREE_PAGES || ret == ESP_ERR_NVS_NEW_VERSION_FOUND) {
         ESP_ERROR_CHECK(nvs_flash_erase());