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/app.h

@@ -0,0 +1,37 @@
+#pragma once
+
+// The objects of the clock firmware and the actions the web UI and Home Assistant use.
+// main.cpp only decides the order of things at boot and in loop().
+
+#include "BROSE9323.h"
+#include "display/frames.h"
+#include "display/status_screen.h"
+#include "logic/display_controller.h"
+#include "logic/settings.h"
+#include "nano_link/nano_link.h"
+
+extern NanoLink nano;
+extern BROSE9323 display;
+extern FlipdotFrames frames;
+extern StatusScreen status;
+extern DisplayController controller;
+
+// Settings: loaded at boot, changed in the web UI
+const Settings &appSettings();
+void appLoadSettings();
+// Validates, stores and applies. Returns nullptr or an error message. Sets
+// restart_needed when the change only works after a restart (Home Assistant).
+const char *appSaveSettings(const Settings &settings, bool &restart_needed);
+
+// The page shown during the day: PAGE_CLOCK or a bitmap name (stored in the settings)
+const char *appSelectPage(const char *name);
+// A bitmap was saved or deleted: redraw when it is the current page
+void appBitmapChanged(const char *name);
+
+// Live mode of the web UI
+void appShowLive(const uint8_t *bitmap);
+void appStopLive();
+
+// Restart the ESP32 after `delay_ms` (so a web response can still be sent)
+void appRestartLater(uint32_t delay_ms);
+void appLoop();