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/logic/builtin_pages.h

@@ -0,0 +1,16 @@
+#pragma once
+
+#include "logic/page.h"
+
+// The built-in dynamic pages. They can't be changed or deleted; the web UI saves an edited
+// copy under a new name.
+//
+//   Clock  Pikachu with the time in a thought bubble, yawning from 17:00 (the clock of
+//          the old firmware; also the default page)
+
+#define BUILTIN_PAGE_CLOCK "Clock"
+
+int builtinPageCount();
+const char *builtinPageName(int index);
+// False when there is no built-in page with this name (compared without case)
+bool builtinPage(const char *name, DynamicPage &page);