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/ha_api.cpp

@@ -0,0 +1,178 @@
+#include "net/ha_api.h"
+
+#include <ArduinoJson.h>
+#include <HTTPClient.h>
+#include <WiFi.h>
+#include <vector>
+
+#include "config.h"
+#include "credentials.h"
+
+struct Entry
+{
+	String entity;
+	String attribute;
+	String value;
+	bool known;
+	bool watched;
+	uint32_t next_poll;
+};
+
+static String base_url;
+static String token;
+static std::vector<Entry> entries;
+// Kept for the editor's previews, besides the watched ones
+static const size_t MAX_ENTRIES = 16;
+
+void haApiSetSettings(const HomeAssistantSettings &settings)
+{
+	if (settings.api_url[0])
+		base_url = settings.api_url;
+	else
+		base_url = String("http://") + (settings.host[0] ? String(settings.host) : BROKER_ADDR.toString()) + ":8123";
+	while (base_url.endsWith("/"))
+		base_url.remove(base_url.length() - 1);
+	token = settings.token;
+	for (Entry &e : entries)
+		e.next_poll = millis(); // read again with the new settings
+}
+
+static Entry *find(const char *entity, const char *attribute)
+{
+	for (Entry &e : entries)
+		if (e.entity == entity && e.attribute == attribute)
+			return &e;
+	return nullptr;
+}
+
+static Entry &add(const char *entity, const char *attribute)
+{
+	Entry *e = find(entity, attribute);
+	if (e)
+		return *e;
+	if (entries.size() >= MAX_ENTRIES)
+		for (auto it = entries.begin(); it != entries.end(); ++it)
+			if (!it->watched)
+			{
+				entries.erase(it);
+				break;
+			}
+	entries.push_back({entity, attribute, "", false, false, millis()});
+	return entries.back();
+}
+
+void haApiWatch(const DynamicPage *page)
+{
+	for (Entry &e : entries)
+		e.watched = false;
+	if (!page)
+		return;
+	for (int i = 0; i < page->element_count; i++)
+	{
+		const PageElement &element = page->elements[i];
+		if (element.type != ElementType::HaValue || !validEntityId(element.entity))
+			continue;
+		Entry &e = add(element.entity, element.attribute);
+		if (!e.watched)
+			e.next_poll = millis();
+		e.watched = true;
+	}
+}
+
+// Blocks at most about 2 x HA_HTTP_TIMEOUT (connect, then the answer)
+static const char *fetch(const String &entity, const String &attribute, String &value)
+{
+	if (!token.length())
+		return "No Home Assistant token set (Home Assistant tab)";
+	if (!WiFi.isConnected())
+		return "No WiFi";
+
+	HTTPClient http;
+	http.setConnectTimeout(HA_HTTP_TIMEOUT);
+	http.setTimeout(HA_HTTP_TIMEOUT);
+	if (!http.begin(base_url + "/api/states/" + entity))
+		return "Invalid Home Assistant URL";
+	http.addHeader("Authorization", "Bearer " + token);
+	int code = http.GET();
+	if (code != 200)
+	{
+		http.end();
+		if (code == 401)
+			return "Home Assistant refused the token";
+		if (code == 404)
+			return "Unknown entity";
+		return code < 0 ? "Home Assistant not reachable" : "Unexpected answer from Home Assistant";
+	}
+
+	JsonDocument filter;
+	if (attribute.length())
+		filter["attributes"][attribute] = true;
+	else
+		filter["state"] = true;
+	JsonDocument doc;
+	DeserializationError error = deserializeJson(doc, http.getString(), DeserializationOption::Filter(filter));
+	http.end();
+	if (error)
+		return "Invalid answer from Home Assistant";
+
+	JsonVariantConst v = doc["state"];
+	if (attribute.length())
+		v = doc["attributes"][attribute];
+	if (v.isNull())
+		return "Unknown attribute";
+	if (v.is<const char *>())
+		value = v.as<const char *>();
+	else
+	{
+		value = "";
+		serializeJson(v, value); // numbers, true/false
+	}
+	return nullptr;
+}
+
+bool haApiLoop(bool wifi_connected)
+{
+	if (!wifi_connected || !token.length())
+		return false;
+	uint32_t now = millis();
+	for (Entry &e : entries)
+	{
+		if (!e.watched || (int32_t)(now - e.next_poll) < 0)
+			continue;
+		e.next_poll = now + HA_POLL_INTERVAL;
+		String value;
+		const char *error = fetch(e.entity, e.attribute, value);
+		if (error)
+		{
+			// Shown as "--" until it can be read again
+			Serial.printf("Home Assistant %s: %s\n", e.entity.c_str(), error);
+			bool changed = e.known;
+			e.known = false;
+			return changed;
+		}
+		bool changed = !e.known || e.value != value;
+		e.value = value;
+		e.known = true;
+		return changed; // one entity per loop()
+	}
+	return false;
+}
+
+const char *haApiValue(const char *entity, const char *attribute)
+{
+	Entry *e = find(entity, attribute);
+	return e && e->known ? e->value.c_str() : nullptr;
+}
+
+const char *haApiFetchNow(const char *entity, const char *attribute, String &value)
+{
+	if (!validEntityId(entity))
+		return "Invalid entity id";
+	const char *error = fetch(entity, attribute, value);
+	if (error)
+		return error;
+	Entry &e = add(entity, attribute);
+	e.value = value;
+	e.known = true;
+	return nullptr;
+}