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/web/web_ui.h

@@ -0,0 +1,22 @@
+#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.
+//
+// JSON API (bitmaps are 418 hex digits, see logic/bitmap_format.h):
+//   GET  /api/status            time, WiFi, firmware, Home Assistant, storage
+//   GET  /api/screen            what the dots show now {on, live, data}
+//   GET  /api/bitmaps           all bitmaps with data {storage, bitmaps:[{name, builtin, data}]}
+//   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}
+//   POST /api/live              show now {data}
+//   POST /api/live/stop
+//   GET  /api/settings          (the MQTT password is never sent, only password_set)
+//   POST /api/settings          changed fields; {settings, restart}
+//   POST /api/restart
+//   POST /api/recovery
+void webUiBegin();
+void webUiLoop();