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_manager.cpp

@@ -0,0 +1,33 @@
+#include "service_manager.h"
+
+namespace roro {
+
+void ServiceManager::add(Service& service) { entries_.push_back({&service, 0, true}); }
+
+void ServiceManager::startAll(uint32_t nowMs) {
+    for (auto& e : entries_) {
+        e.service->start();
+        e.lastTickMs = nowMs;
+        e.due = true;
+    }
+    running_ = true;
+}
+
+void ServiceManager::stopAll() {
+    for (auto it = entries_.rbegin(); it != entries_.rend(); ++it) it->service->stop();
+    running_ = false;
+}
+
+void ServiceManager::tick(uint32_t nowMs) {
+    if (!running_) return;
+    for (auto& e : entries_) {
+        // Unsigned subtraction keeps working across the 49-day millis() wraparound.
+        if (e.due || nowMs - e.lastTickMs >= e.service->tickIntervalMs()) {
+            e.due = false;
+            e.lastTickMs = nowMs;
+            e.service->tick(nowMs);
+        }
+    }
+}
+
+}  // namespace roro