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/logic/settings.cpp

@@ -0,0 +1,58 @@
+#include "logic/settings.h"
+
+#include <stdio.h>
+#include <string.h>
+
+#include "logic/bitmap_format.h"
+
+static bool terminated(const char *text, int size)
+{
+	return memchr(text, '\0', size) != nullptr;
+}
+
+const char *validateSettings(const Settings &s)
+{
+	if (!terminated(s.page, sizeof(s.page)) ||
+		(strcmp(s.page, PAGE_CLOCK) != 0 && !validBitmapName(s.page)))
+		return "Unknown page";
+
+	const ScheduleSettings &t = s.schedule;
+	if (t.day_start >= MINUTES_PER_DAY || t.late_start > MINUTES_PER_DAY || t.night_start > MINUTES_PER_DAY)
+		return "Times must be between 00:00 and 24:00";
+	if (t.day_start > t.late_start || t.late_start > t.night_start)
+		return "The times must be in order: day start, late evening, night";
+
+	if (s.clock.evening_start >= MINUTES_PER_DAY)
+		return "The evening must start before 24:00";
+
+	if (s.flip_time < SETTINGS_FLIP_TIME_MIN || s.flip_time > SETTINGS_FLIP_TIME_MAX)
+		return "The flip time must be between 50 and 2000 us";
+
+	const HomeAssistantSettings &ha = s.home_assistant;
+	if (!terminated(ha.host, sizeof(ha.host)) || !terminated(ha.user, sizeof(ha.user)) ||
+		!terminated(ha.password, sizeof(ha.password)))
+		return "Home Assistant text too long";
+	if (ha.port == 0)
+		return "Invalid MQTT port";
+
+	return nullptr;
+}
+
+bool parseTime(const char *text, uint16_t &minutes)
+{
+	if (text == nullptr)
+		return false;
+	int hour = 0, minute = 0;
+	char extra;
+	if (sscanf(text, "%d:%d%c", &hour, &minute, &extra) != 2)
+		return false;
+	if (hour < 0 || minute < 0 || minute > 59 || hour * 60 + minute > MINUTES_PER_DAY)
+		return false;
+	minutes = hour * 60 + minute;
+	return true;
+}
+
+void formatTime(uint16_t minutes, char *out)
+{
+	snprintf(out, 6, "%02u:%02u", (unsigned)(minutes / 60) % 100, (unsigned)(minutes % 60));
+}