Add HA dropdowns, off image, flip fixes and refresh effects

Home Assistant: remove the Clock switch (its entity is deleted on connect),
add an IP sensor and Mode / Off image dropdowns whose options follow the
saved bitmaps. Remove the built-in "Nintendo border" bitmap.

Off image: a bitmap (or blank) left on the dots when the display switches off.

Nano: pause after each flip pulse and repeat pulses for changed dots, both
stored in EEPROM (G/N commands). Refresh effects (E command): instant,
sparkle, wipe, rain, from the middle out, diagonal, spiral, flip all then
reveal, push and random, optionally only for small changes. Effects run in
steps from loop() so serial input keeps flowing.

Web UI: flip settings, refresh effect and test patterns under Settings; the
System tab shows why the ESP32 last restarted. Settings records from
versions 1 and 2 are migrated. Firmware 2.3.0.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CLAUDE.md

@@ -36,7 +36,7 @@ See README.md for the overview.
   data in `PROGMEM`.
 - The ESP32 talks to the Nano on `Serial2` (owned by `NanoLink`, GPIO 17 TX / GPIO 16 RX).
   `Serial` (UART0/USB) is free for debug output. Never write debug text to `Serial2`: the
-  Nano runs lines that start with s/S/F/D/P/B/R/T as commands.
+  Nano runs lines that start with s/S/F/D/P/B/R/T/G/N/E as commands.
 - Open hardware TODOs are listed in the README `TODO` section. Update it when one is done.
 - `src/esp32/secrets.h` holds the real credentials and is gitignored. Never commit it.
   Add new secrets to `secrets.example.h` as placeholders.