Add widget kit, input layer with Compose Key, Launcher and demo apps

Steps 5 and 6 of M0.
- lib/ui (host-tested): ListModel, LineEditor (UTF-8, byte-limited),
  wrapText, ToastQueue, DialogModel
- lib/input (host-tested): KeyMapper turns keyboard state into logical
  keys (Fn arrows, ` Back, Fn+` Home) and composes accents with opt
- src/ui: off-screen 16-bit frame pushed in one transfer (fixes the
  flicker), Status Bar, list, text, line editor, dialog, Toast widgets,
  Notifier (Toast + beep + LED), vendored public-domain Latin-1 fonts
- Apps: minimal Launcher, Widget demo, Diagnostics (SD erase now
  behind a confirmation dialog)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01EhqxQ49eCju4CzKYNjZzwT

src/ui/fonts.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <M5GFX.h>
+
+namespace roro {
+
+namespace fontdata {
+extern const uint8_t _6x13_tf[];
+extern const uint8_t _6x13B_tf[];
+extern const uint8_t _5x8_tf[];
+}  // namespace fontdata
+
+// Latin-1 bitmap fonts (accented letters included).
+namespace fonts {
+inline const lgfx::U8g2font body(fontdata::_6x13_tf);   // 6x13
+inline const lgfx::U8g2font bold(fontdata::_6x13B_tf);  // 6x13 bold
+inline const lgfx::U8g2font small(fontdata::_5x8_tf);   // 5x8, Status Bar
+}  // namespace fonts
+
+}  // namespace roro