Add core runtime: event bus, services, app lifecycle

lib/core is hardware-independent and unit-tested on the host:
- EventBus: fixed-size thread-safe queue, delivered on the UI task by
  dispatch(); drops newest when full and counts drops
- Service / ServiceManager: cooperative ticking at per-service intervals,
  no catch-up bursts, safe across millis() wraparound
- App / AppManager: one foreground App, Home always to Launcher, Back
  offered to the App first, hidden Apps, redraw requests
- KeyEvent: logical keys for the upcoming input layer

Firmware main loop now ticks services and dispatches events.

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

lib/core/src/key_event.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <cstdint>
+
+namespace roro {
+
+// Logical keys, already translated from the physical keyboard (Fn combos, Esc position, etc.).
+enum class Key : uint8_t {
+    Char,  // a printable character in `ch` (Unicode code point, accents already composed)
+    Up,
+    Down,
+    Left,
+    Right,
+    Select,
+    Back,
+    Home,
+    Tab,
+    Delete,
+};
+
+struct KeyEvent {
+    Key key = Key::Char;
+    uint32_t ch = 0;
+    bool shift = false;
+    bool ctrl = false;
+    bool alt = false;
+
+    static KeyEvent of(Key key) {
+        KeyEvent e;
+        e.key = key;
+        return e;
+    }
+
+    static KeyEvent character(uint32_t codePoint) {
+        KeyEvent e;
+        e.ch = codePoint;
+        return e;
+    }
+};
+
+}  // namespace roro