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>

sdkconfig.defaults

@@ -1,5 +1,5 @@
-# Elecrow CrowPanel 7.0" HMI -- ESP32-S3-WROOM-1-N4R8
-# 4MB flash, 8MB octal PSRAM, 800x480 RGB panel.
+# Elecrow CrowPanel 7.0" Advance HMI -- ESP32-S3-WROOM-1-N16R8
+# 16MB flash, 8MB octal PSRAM, 800x480 RGB panel.
 
 CONFIG_IDF_TARGET="esp32s3"