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/display/bitmap_store.h

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <Arduino.h>
+#include <vector>
+
+#include "logic/bitmap_format.h"
+
+// Full screen bitmaps (84 x 19, see logic/bitmap_format.h): built-in ones from
+// display/bitmaps.h and the ones uploaded in the web UI, stored on LittleFS
+// (partition "spiffs" in partitions.csv) as /bitmaps/<name>.bin.
+
+struct BitmapInfo
+{
+	String name;
+	bool builtin;
+};
+
+const int MAX_BITMAPS = 200;
+
+// Mounts LittleFS (formats it the first time). False without the partition (old flash
+// layout): only the built-in bitmaps are available then.
+bool bitmapStoreBegin();
+bool bitmapStorageAvailable();
+void bitmapStorageUsage(size_t &used, size_t &total);
+
+std::vector<BitmapInfo> listBitmaps();
+bool bitmapExists(const char *name);
+bool loadBitmap(const char *name, uint8_t *bitmap);
+
+// Return nullptr on success, otherwise a message for the user
+const char *saveBitmap(const char *name, const uint8_t *bitmap);
+const char *deleteBitmap(const char *name);