Add a web UI to the clock firmware

- Web UI on port 80: live view of the display, choose the page (clock or
  a bitmap), bitmaps (list, show, live, edit, delete), draw / image upload
  with conversion in the browser, live mode, settings, Home Assistant
- Live view from a shadow buffer in the BROSE9323 driver (shownPixel)
- Settings in NVS with the original behaviour as defaults: schedule times,
  quarter hours, yawning Pikachu, No WiFi screen, flip time, status LED,
  Home Assistant broker (restart on change)
- Bitmaps on LittleFS; new 320 KB partition, ota slots now 1.31 MB
- DisplayController: pages, live mode, settings; app.cpp holds the objects
- README for the recovery app; docs for the web UI
- Tests: settings, time parsing, bitmap format and names, schedule with
  settings, pages and live mode (95 total)

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

src/esp32/net/home_assistant.h

@@ -1,14 +1,19 @@
 #pragma once
 
 #include "logic/display_controller.h"
+#include "logic/settings.h"
 
 // Home Assistant integration over MQTT (with discovery):
 //   FlipDot Display Clock     switch: on = clock, off = Nintendo logo
 //   FlipDot Display Power     switch: off = clear the display and switch it off
 //   FlipDot Display Firmware  sensor: version and health, e.g. "2.1.0, ok, 0 crashes, ..."
 //   FlipDot Display Recovery  button: restart into the recovery app (for 10 minutes)
-void homeAssistantBegin(DisplayController &controller);
+//
+// The broker comes from the settings (web UI); an empty host means BROKER_ADDR, MQTT_USER
+// and MQTT_PASSWORD from secrets.h. Changes need a restart.
+void homeAssistantBegin(DisplayController &controller, const HomeAssistantSettings &settings);
 void homeAssistantLoop();
+bool homeAssistantConnected();
 
 // Publish the firmware status (only sent when it changes, and again after a reconnect)
 void homeAssistantSetFirmwareStatus(const char *status);