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.cpp

@@ -0,0 +1,131 @@
+#include "display/bitmap_store.h"
+
+#include <LittleFS.h>
+#include <strings.h>
+
+#include "display/bitmaps.h"
+
+static const char *DIR = "/bitmaps";
+
+struct BuiltinBitmap
+{
+	const char *name;
+	const uint8_t *data; // PROGMEM, BITMAP_BYTES
+};
+
+static const BuiltinBitmap BUILTIN[] = {
+	{"Nintendo", nintendo_bitmap_Nintendo_new},
+	{"Nintendo border", nintendo_bitmap_nintendo_border},
+};
+
+static bool mounted = false;
+
+static const BuiltinBitmap *builtin(const char *name)
+{
+	for (const BuiltinBitmap &b : BUILTIN)
+		if (strcasecmp(b.name, name) == 0)
+			return &b;
+	return nullptr;
+}
+
+static String path(const char *name)
+{
+	return String(DIR) + "/" + name + ".bin";
+}
+
+bool bitmapStoreBegin()
+{
+	mounted = LittleFS.begin(true);
+	if (mounted && !LittleFS.exists(DIR))
+		LittleFS.mkdir(DIR);
+	Serial.printf("Bitmap storage %s\n", mounted ? "ready" : "not available (old flash layout?)");
+	return mounted;
+}
+
+bool bitmapStorageAvailable()
+{
+	return mounted;
+}
+
+void bitmapStorageUsage(size_t &used, size_t &total)
+{
+	used = mounted ? LittleFS.usedBytes() : 0;
+	total = mounted ? LittleFS.totalBytes() : 0;
+}
+
+std::vector<BitmapInfo> listBitmaps()
+{
+	std::vector<BitmapInfo> list;
+	for (const BuiltinBitmap &b : BUILTIN)
+		list.push_back({b.name, true});
+	if (!mounted)
+		return list;
+
+	File dir = LittleFS.open(DIR);
+	for (File file = dir.openNextFile(); file; file = dir.openNextFile())
+	{
+		String name = file.name();
+		int slash = name.lastIndexOf('/');
+		if (slash >= 0)
+			name = name.substring(slash + 1);
+		if (!name.endsWith(".bin"))
+			continue;
+		name.remove(name.length() - 4);
+		if (validBitmapName(name.c_str()) && !builtin(name.c_str()))
+			list.push_back({name, false});
+	}
+	return list;
+}
+
+bool bitmapExists(const char *name)
+{
+	if (builtin(name))
+		return true;
+	return mounted && validBitmapName(name) && LittleFS.exists(path(name));
+}
+
+bool loadBitmap(const char *name, uint8_t *bitmap)
+{
+	const BuiltinBitmap *b = builtin(name);
+	if (b)
+	{
+		memcpy_P(bitmap, b->data, BITMAP_BYTES);
+		return true;
+	}
+	if (!mounted || !validBitmapName(name))
+		return false;
+	File file = LittleFS.open(path(name), "r");
+	if (!file)
+		return false;
+	bool ok = file.read(bitmap, BITMAP_BYTES) == (size_t)BITMAP_BYTES;
+	file.close();
+	return ok;
+}
+
+const char *saveBitmap(const char *name, const uint8_t *bitmap)
+{
+	if (!validBitmapName(name))
+		return "Invalid name: use 1-24 letters, digits, spaces, - or _";
+	if (builtin(name))
+		return "A built-in bitmap has this name";
+	if (!mounted)
+		return "No bitmap storage (install the new flash layout over USB, see README)";
+	if (!LittleFS.exists(path(name)) && listBitmaps().size() >= (size_t)MAX_BITMAPS + (sizeof(BUILTIN) / sizeof(BUILTIN[0])))
+		return "Too many bitmaps, delete some first";
+
+	File file = LittleFS.open(path(name), "w");
+	if (!file)
+		return "Could not write the file";
+	bool ok = file.write(bitmap, BITMAP_BYTES) == (size_t)BITMAP_BYTES;
+	file.close();
+	return ok ? nullptr : "Storage full";
+}
+
+const char *deleteBitmap(const char *name)
+{
+	if (builtin(name))
+		return "Built-in bitmaps can't be deleted";
+	if (!mounted || !validBitmapName(name) || !LittleFS.exists(path(name)))
+		return "Bitmap not found";
+	return LittleFS.remove(path(name)) ? nullptr : "Could not delete the file";
+}