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/apps/demo_app.cpp

@@ -0,0 +1,110 @@
+#include "demo_app.h"
+
+#include "ui/widgets.h"
+
+namespace roro {
+
+namespace {
+const char* const kMenu[] = {"Text view", "Line editor", "Dialog", "Toast: info", "Toast: warning",
+                             "Toast: burst of 5"};
+const char* const kText =
+    "Bienvenue sur roro9stack ! Ce texte teste le retour \xC3\xA0 la ligne automatique et les "
+    "accents : \xC3\xA9t\xC3\xA9, \xC3\xA0 bient\xC3\xB4t, gar\xC3\xA7on, No\xC3\xABl, "
+    "ma\xC3\xAEtre, o\xC3\xB9.\n\n"
+    "Use Fn+; and Fn+. to scroll, ` to go back. Fn+` always returns to the Launcher.\n\n"
+    "Unbreakablewordthatislongerthanawholelineofthescreen to test hard breaks.";
+}  // namespace
+
+void DemoApp::onEnter() {
+    page_ = Page::Menu;
+    dialog_.reset();
+    menu_.setCount(sizeof(kMenu) / sizeof(kMenu[0]));
+}
+
+void DemoApp::notify(const char* text, NotificationLevel level) {
+    bus_.publish(Event::withText(EventType::Notification, text, static_cast<int32_t>(level)));
+}
+
+bool DemoApp::onKey(const KeyEvent& e) {
+    requestRedraw();
+    if (dialog_) {
+        dialog_->onKey(e);
+        int r = dialog_->result();
+        if (r != DialogModel::kPending) {
+            notify(r == DialogModel::kCancelled ? "Dialog cancelled" : ("Chose " + dialog_->buttons()[r]).c_str(),
+                   NotificationLevel::Info);
+            dialog_.reset();
+        }
+        return true;
+    }
+    switch (page_) {
+        case Page::Menu: return onMenuKey(e);
+        case Page::Text:
+            if (e.key == Key::Up && textScroll_ > 0) textScroll_--;
+            else if (e.key == Key::Down && textScroll_ < textLineCount_ - 1) textScroll_++;
+            else if (e.key == Key::Back) page_ = Page::Menu;
+            return true;
+        case Page::Editor:
+            switch (e.key) {
+                case Key::Char: editor_.insert(e.ch); break;
+                case Key::Delete: editor_.backspace(); break;
+                case Key::Left: editor_.left(); break;
+                case Key::Right: editor_.right(); break;
+                case Key::Up: editor_.home(); break;
+                case Key::Down: editor_.end(); break;
+                case Key::Select:
+                    if (!editor_.text().empty()) notify(editor_.text().c_str(), NotificationLevel::Message);
+                    break;
+                case Key::Back: page_ = Page::Menu; break;
+                default: break;
+            }
+            return true;
+    }
+    return false;
+}
+
+bool DemoApp::onMenuKey(const KeyEvent& e) {
+    switch (e.key) {
+        case Key::Up: menu_.up(); return true;
+        case Key::Down: menu_.down(); return true;
+        case Key::Select: break;
+        default: return false;  // Back leaves the App
+    }
+    switch (menu_.selected()) {
+        case 0: page_ = Page::Text; textScroll_ = 0; break;
+        case 1: page_ = Page::Editor; break;
+        case 2: dialog_.reset(new DialogModel({"Cancel", "Maybe", "OK"})); break;
+        case 3: notify("Hello from the demo", NotificationLevel::Info); break;
+        case 4: notify("Something needs attention", NotificationLevel::Warning); break;
+        case 5:
+            for (int i = 1; i <= 5; i++) notify(("Burst " + std::to_string(i)).c_str(), NotificationLevel::Info);
+            break;
+    }
+    return true;
+}
+
+void DemoApp::draw(Canvas& c) {
+    const auto& area = theme::kContent;
+    switch (page_) {
+        case Page::Menu:
+            widgets::list(c, menu_, area, [](int i) { return std::string(kMenu[i]); });
+            break;
+        case Page::Text: {
+            auto lines = wrapText(kText, area.w - 10, widgets::bodyMeasure(c));
+            textLineCount_ = static_cast<int>(lines.size());
+            widgets::textLines(c, lines, textScroll_, area);
+            break;
+        }
+        case Page::Editor:
+            c.setTextColor(theme::kMuted);
+            c.drawString("Type (opt ' e = \xC3\xA9). Enter: toast", 4, area.y + 4);
+            widgets::lineEditor(c, editor_, {4, area.y + 22, area.w - 8, 0});
+            c.setTextColor(theme::kMuted);
+            c.drawString((std::to_string(editor_.text().size()) + "/39 bytes").c_str(), 4, area.y + 44);
+            break;
+    }
+    if (dialog_)
+        widgets::dialog(c, "Dialog", "Left/Right or Tab to choose, Enter to confirm, ` to cancel.", *dialog_);
+}
+
+}  // namespace roro