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

src/main.cpp

@@ -1,8 +1,13 @@
 // roro9stack — boot stub: proves toolchain, display and keyboard.
 #include <M5Cardputer.h>
 
+#include "event_bus.h"
+#include "service_manager.h"
 #include "version.h"
 
+static roro::EventBus bus;
+static roro::ServiceManager services;
+
 void setup() {
     auto cfg = M5.config();
     M5Cardputer.begin(cfg, true);  // true = enable keyboard
@@ -19,6 +24,7 @@ void setup() {
     d.drawString("Press keys...", 8, 56);
 
     Serial.begin(115200);
+    services.startAll(millis());
 }
 
 static void printStatus() {
@@ -34,6 +40,9 @@ void loop() {
         printStatus();
     }
 
+    services.tick(millis());
+    bus.dispatch();
+
     M5Cardputer.update();
     if (M5Cardputer.Keyboard.isChange() && M5Cardputer.Keyboard.isPressed()) {
         auto state = M5Cardputer.Keyboard.keysState();