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/drivers/display/display_rgb.c

@@ -87,14 +87,6 @@ static const char *TAG = "display_rgb";
 static esp_lcd_panel_handle_t panel = NULL;
 static lv_display_t *disp = NULL;
 
-/*
- * Partial-mode flush: blit the dirty rectangle from a small internal-RAM
- * draw buffer into the single PSRAM framebuffer.
- *
- * Page-flipping two framebuffers instead would be cheaper, but the swap
- * lands mid-scanout on this panel and tears visibly. Copying into one
- * framebuffer that the LCD scans continuously is what the vendor driver does.
- */
 /*
  * Double-buffered flush.
  *