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>

partitions.csv

@@ -2,11 +2,12 @@
 #
 #   factory  recovery app (src/recovery): WiFi setup portal + OTA, never changed by OTA
 #   ota_0/1  clock firmware (src/esp32), updated over OTA in turns, with rollback
+#   spiffs   LittleFS for the bitmaps uploaded in the web UI
 #
 # Name,   Type, SubType,  Offset,   Size
 nvs,      data, nvs,      0x9000,   0x5000
 otadata,  data, ota,      0xe000,   0x2000
 factory,  app,  factory,  0x10000,  0x100000
-ota_0,    app,  ota_0,    0x110000, 0x170000
-ota_1,    app,  ota_1,    0x280000, 0x170000
-coredump, data, coredump, 0x3F0000, 0x10000
+ota_0,    app,  ota_0,    0x110000, 0x150000
+ota_1,    app,  ota_1,    0x260000, 0x150000
+spiffs,   data, spiffs,   0x3B0000, 0x50000