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/display/font_store.cpp

@@ -0,0 +1,114 @@
+#include "display/font_store.h"
+
+#include <LittleFS.h>
+#include <map>
+
+#include "display/bitmap_store.h"
+#include "logic/bitmap_format.h"
+#include "logic/builtin_fonts.h"
+
+static const char *DIR = "/fonts";
+static const char *EXTENSION = ".fnt";
+
+static uint32_t revision = 0;
+// Loaded fonts by name; cleared when a font is saved or deleted
+static std::map<String, std::vector<uint8_t>> cache;
+
+static String path(const char *name)
+{
+	return String(DIR) + "/" + name + EXTENSION;
+}
+
+std::vector<FontInfo> listFonts()
+{
+	std::vector<FontInfo> list;
+	for (int i = 0; i < BUILTIN_FONT_COUNT; i++)
+		list.push_back({BUILTIN_FONTS[i].name, true, (uint8_t)fontHeight(builtinFont(BUILTIN_FONTS[i]))});
+	for (const String &name : storedNames(DIR, EXTENSION))
+		if (!findBuiltinFont(name.c_str()))
+			list.push_back({name, false, (uint8_t)fontHeight(findFont(name.c_str()))});
+	return list;
+}
+
+uint32_t fontListRevision()
+{
+	return revision;
+}
+
+bool fontExists(const char *name)
+{
+	if (findBuiltinFont(name))
+		return true;
+	return bitmapStorageAvailable() && validBitmapName(name) && LittleFS.exists(path(name));
+}
+
+Font findFont(const char *name)
+{
+	const BuiltinFont *builtin = findBuiltinFont(name);
+	if (builtin)
+		return builtinFont(*builtin);
+
+	Font font;
+	if (!bitmapStorageAvailable() || !validBitmapName(name))
+		return font;
+	auto cached = cache.find(name);
+	if (cached == cache.end())
+	{
+		if (cache.size() >= 16)
+			cache.clear();
+		std::vector<uint8_t> data;
+		File file;
+		if (LittleFS.exists(path(name))) // open() logs an error for a missing file
+			file = LittleFS.open(path(name), "r");
+		if (file && file.size() <= FONT_MAX_SIZE)
+		{
+			data.resize(file.size());
+			if (file.read(data.data(), data.size()) != data.size() || !validFont(data.data(), data.size()))
+				data.clear();
+		}
+		if (file)
+			file.close();
+		cached = cache.emplace(name, std::move(data)).first; // also remembers a missing font
+	}
+	if (!cached->second.empty())
+	{
+		font.data = cached->second.data();
+		font.size = cached->second.size();
+	}
+	return font;
+}
+
+const char *saveFont(const char *name, const uint8_t *data, size_t size)
+{
+	if (!validBitmapName(name))
+		return "Invalid name: use 1-24 letters, digits, spaces, - or _";
+	if (findBuiltinFont(name))
+		return "A built-in font has this name";
+	if (!validFont(data, size))
+		return "Invalid font data";
+	if (!bitmapStorageAvailable())
+		return "No storage (install the new flash layout over USB, see README)";
+	if (!LittleFS.exists(path(name)) && storedNames(DIR, EXTENSION).size() >= (size_t)MAX_FONTS)
+		return "Too many fonts, delete some first";
+
+	File file = LittleFS.open(path(name), "w");
+	bool ok = file && file.write(data, size) == size;
+	if (file)
+		file.close();
+	cache.clear();
+	revision++;
+	return ok ? nullptr : "Could not write the file (storage full?)";
+}
+
+const char *deleteFont(const char *name)
+{
+	if (findBuiltinFont(name))
+		return "Built-in fonts can't be deleted";
+	if (!bitmapStorageAvailable() || !validBitmapName(name) || !LittleFS.exists(path(name)))
+		return "Font not found";
+	if (!LittleFS.remove(path(name)))
+		return "Could not delete the file";
+	cache.clear();
+	revision++;
+	return nullptr;
+}