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>

src/esp32/app.h

@@ -25,7 +25,9 @@ const char *appSaveSettings(const Settings &settings, bool &restart_needed);
 
 // The page shown during the day: PAGE_CLOCK or a bitmap name (stored in the settings)
 const char *appSelectPage(const char *name);
-// A bitmap was saved or deleted: redraw when it is the current page
+// Left on the dots when the display switches off: OFF_PAGE_BLANK or a bitmap name
+const char *appSelectOffPage(const char *name);
+// A bitmap was saved or deleted: redraw when it is the current page or off image
 void appBitmapChanged(const char *name);
 
 // Live mode of the web UI