Add scrolling, countdown, stopwatch, images, seconds, multiplier and degree sign

- Text elements can scroll in a window at a set speed; clock, countdown and
  stopwatch can show seconds. Moving pages are sent as instant frames (new
  Nano command D1) and paced by the estimated flip time.
- Countdown to a date and time (smart, days, days + time, with seconds),
  stopwatch (web UI, HA switch and reset button), image element (fixed or
  by Home Assistant state), multiplier for HA values, degree sign (char 127)
  in all fonts and the font converter.
- Page format version 2; version 1 pages are converted.

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

src/esp32/display/bitmap_store.cpp

@@ -110,7 +110,8 @@ bool loadBitmap(const char *name, uint8_t *bitmap)
 		memcpy_P(bitmap, b->data, BITMAP_BYTES);
 		return true;
 	}
-	if (!mounted || !validBitmapName(name))
+	// Checked first: open() logs an error for a missing file (images try names by state)
+	if (!mounted || !validBitmapName(name) || !LittleFS.exists(path(name)))
 		return false;
 	File file = LittleFS.open(path(name), "r");
 	if (!file)