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>

CLAUDE.md

@@ -126,6 +126,21 @@ See README.md for the overview.
 - Arduino's `esp_app_desc_t` version and date come from the precompiled core, so the
   clock firmware stores `FIRMWARE_VERSION` per slot in NVS for the recovery page.
 
+## ESP32 web UI
+
+- `app.cpp` owns the objects and the actions (settings, page, live mode, restart);
+  `web/web_ui.cpp` is the JSON API (endpoints listed in `web_ui.h`), `web/web_page.h` the
+  single HTML/JS page (raw string literal in PROGMEM). Keep image work in the browser; the
+  ESP32 only handles 418-character hex bitmaps (`logic/bitmap_format.h`, MSB = left dot).
+- Settings: `logic/settings.h` struct with defaults = original behaviour, stored as an NVS
+  blob with a version (`system/settings_store.cpp`). When the struct changes, bump
+  `VERSION` there (old records then fall back to defaults).
+- Bitmaps on LittleFS in the `spiffs` partition (`/bitmaps/<name>.bin`, 209 bytes). Names
+  are restricted (`validBitmapName`), which also makes them safe in paths and JSON.
+- The display mirror comes from the driver's shadow buffer (`BROSE9323::shownPixel`).
+- Check the page's JavaScript after changes: extract the `<script>` part and run
+  `node --check` on it (node is installed).
+
 ## Git
 
 - Remote: https://mangavalk.com/mangavalk/Flipdot-display.git, branch `main`.