Launcher: a grid of icons, with badges; the list stays as a Setting

The Launcher shows the Apps as a 4 x 3 grid of 32 x 32 icons, the
selected one's name under it (issue #9). The icons are the website's
own, doubled, and two drawn the same way for SSH and the Shell; they
are PNGs in assets/icons, turned into arrays by scripts/make_icons.py,
which CI checks. The selected tile is the website's: dark blue on cyan,
with notched corners.

- GridModel (lib/ui, host-tested) holds the selection and the scrolling.
- App::badge(): a dot on the tile for unread IRC messages, a Track
  recording, a Capture running, an SSH session open.
- Settings > Launcher: Grid or List.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0162FokPdvY2KsS4NBfwyWPk

lib/core/src/app.h

@@ -50,6 +50,10 @@ class App {
     virtual bool retainsContent() const { return false; }
     virtual void contentLost() {}
 
+    // True while something goes on in the App that is worth a look, whether it is in front or
+    // not (unread messages, a recording running): the Launcher marks its tile (issue #9).
+    virtual bool badge() const { return false; }
+
     void requestRedraw() { redraw_ = true; }
 
     bool consumeRedraw() {