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/main.c

@@ -1,3 +1,4 @@
+#include <math.h>
 #include <stdio.h>
 #include <string.h>
 
@@ -54,7 +55,9 @@ static void weather_update_task(void *arg)
             snprintf(detail, sizeof(detail), "%.0f%% humidity",
                      weather.has_humidity ? weather.humidity : 0.0f);
 
-            ui_update_weather((int16_t)(weather.temp_f + 0.5f),
+            /* lroundf, not +0.5f-and-truncate: the latter rounds toward zero
+             * below 0°F, turning -10.6 into -10. */
+            ui_update_weather((int16_t)lroundf(weather.temp_f),
                               weather.has_humidity ? detail : "Outdoor");
 
             wifi_get_status(line, sizeof(line));
@@ -83,7 +86,7 @@ void app_main(void)
      */
     const esp_err_t wifi_err = wifi_init_sta();
     if (wifi_err != ESP_OK) {
-        ESP_LOGE(TAG, "WiFi failed -- continuing, weather will be disabled");
+        ESP_LOGE(TAG, "WiFi not up yet -- weather starts when it connects");
     }
 
     /* LVGL core must exist before the display and touch drivers register
@@ -114,15 +117,22 @@ void app_main(void)
     vTaskDelay(pdMS_TO_TICKS(100));
     ESP_ERROR_CHECK(backlight_set(255));
 
-    if (wifi_err != ESP_OK) {
-        ui_set_status("WiFi: failed");
+    if (wifi_err == ESP_OK) {
+        char status[96];
+        wifi_get_status(status, sizeof(status));
+        ui_set_status(status);
+    } else if (wifi_err == ESP_FAIL || wifi_err == ESP_ERR_TIMEOUT) {
+        /* The event handler keeps retrying in the background; the weather
+         * task polls wifi_is_connected(), so start it anyway rather than
+         * permanently disabling weather because boot raced a slow AP. */
+        ui_set_status("WiFi: connecting...");
+    } else {
+        /* No SSID configured (or setup failed outright) -- nothing will ever
+         * connect, so there is no point starting the weather task. */
+        ui_set_status("WiFi: not configured");
         return;
     }
 
-    char status[96];
-    wifi_get_status(status, sizeof(status));
-    ui_set_status(status);
-
     if (weather_init() != ESP_OK) {
         ui_set_status("Weather: no API credentials");
         return;