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

lib/ui/src/text_wrap.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <functional>
+#include <string>
+#include <vector>
+
+namespace roro {
+
+using MeasureText = std::function<int(const std::string&)>;
+
+// Splits UTF-8 text into lines no wider than maxWidth: breaks at spaces when possible, inside
+// words only when a word alone is too wide, never inside a character. '\n' forces a break.
+std::vector<std::string> wrapText(const std::string& text, int maxWidth, const MeasureText& measure);
+
+}  // namespace roro