Add dynamic pages with clock, date, Home Assistant values and fonts

The hardcoded clock is now the built-in dynamic page "Clock". A dynamic page
has a background bitmap per time of day and up to 8 elements (clock, date,
Home Assistant value, text), each with position, alignment, font and overlay.
Pages are drawn on the ESP32, also for the web previews.

- Pages tab in the web UI: page editor with drag and drop, font upload
  (TTF/OTF converted in the browser to the FDF1 dot font format)
- Built-in fonts Small, Normal, Large and Full height (generated by
  tools/make_builtin_fonts.py), built-in bitmaps Pikachu and Pikachu yawning
- Home Assistant values over the REST API (URL and token in the HA tab)
- Settings version 4: evening settings removed (now time slots of the Clock
  page), old records are converted
- HA Mode dropdown lists the dynamic pages and bitmaps

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

src/esp32/net/home_assistant.h

@@ -5,7 +5,8 @@
 
 // Home Assistant integration over MQTT (with discovery):
 //   FlipDot Display Power     switch: off = draw the off image and switch the display off
-//   FlipDot Display Mode      select: the page shown during the day ("Clock" or a bitmap)
+//   FlipDot Display Mode      select: the page shown during the day (a dynamic page, e.g.
+//                                     the built-in "Clock", or a bitmap)
 //   FlipDot Display Off image select: left on the dots when the display switches off
 //                                     ("Blank" or a bitmap)
 //   FlipDot Display IP        sensor: the IP address