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/web/web_ui.h

@@ -1,8 +1,8 @@
 #pragma once
 
 // Web UI of the clock firmware on port 80 (http://<ESP32 IP>/): live view of the display,
-// choosing the page, bitmaps (upload, draw, store), live mode, settings and Home
-// Assistant. The page itself is in web/web_page.h.
+// choosing the page, dynamic pages and fonts, bitmaps (upload, draw, store), live mode,
+// settings and Home Assistant. The page itself is in web/web_page.h.
 //
 // JSON API (bitmaps are 418 hex digits, see logic/bitmap_format.h):
 //   GET  /api/status            time, WiFi, firmware, Home Assistant, storage
@@ -11,10 +11,18 @@
 //   GET  /api/bitmap?name=      one bitmap {name, data}
 //   POST /api/bitmap            store {name, data}
 //   POST /api/bitmap/delete     {name}
-//   POST /api/page              {page: "clock" or a bitmap name}
+//   GET  /api/pages             dynamic pages {pages:[{name, builtin, page, data (preview)}]}
+//   POST /api/pages/save        {name, page} (page format: web/page_json.h)
+//   POST /api/pages/delete      {name}
+//   POST /api/pages/preview     {page, time ("HH:MM", optional)} -> {data, boxes:[[x,y,w,h]]}
+//   GET  /api/fonts             {fonts:[{name, builtin, height}]}
+//   POST /api/fonts/save        {name, data (hex, format of logic/font.h)}
+//   POST /api/fonts/delete      {name}
+//   GET  /api/ha/value?entity=&attribute=  read a Home Assistant value now {value}
+//   POST /api/page              {page: a dynamic page or bitmap name}
 //   POST /api/live              show now {data}
 //   POST /api/live/stop
-//   GET  /api/settings          (the MQTT password is never sent, only password_set)
+//   GET  /api/settings          (the MQTT password and HA token are never sent, only *_set)
 //   POST /api/settings          changed fields; {settings, restart}
 //   POST /api/restart
 //   POST /api/recovery