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/service.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include <cstdint>
+
+namespace roro {
+
+// A long-lived background capability (see CONTEXT.md). Services are ticked cooperatively from the
+// main loop; one that needs real concurrency (e.g. the radio) may run its own task internally and
+// report through the EventBus.
+class Service {
+   public:
+    virtual ~Service() = default;
+    virtual const char* name() const = 0;
+    virtual void start() {}
+    virtual void stop() {}
+    virtual void tick(uint32_t nowMs) { (void)nowMs; }
+    virtual uint32_t tickIntervalMs() const { return 1000; }
+};
+
+}  // namespace roro