Metronome/phrase click unification: run-driven beats, gated widget

- Phrase Mode (sync to metronome): the run's scheduler is the single click
  source (with count-in); the metronome widget is muted and its pendulum
  mirrors the run's beats via the new phraseBeatBus (audio-timestamp
  scheduled). No more double clicks; clicks only while the run is active
  (phraseRunBus gates the widget's own ticking).
- Schedule entries now carry continuous beat index + accent flag (downbeats
  accented, count-in beat 1 accented).
- 'At your pace': optional click via the metronome toggle (kept explicit).
- Metronome widget: gate prop; in gated mode it listens to the beat bus
  instead of running its own scheduler.

src/hooks/phraseRunBus.ts

@@ -0,0 +1,26 @@
+/**
+ * Tiny pub/sub for the phrase trainer's running state.
+ *
+ * Lets the (global) metronome widget gate its pendulum/click on the phrase
+ * run: in Phrase Mode the metronome should only be active while the trainer
+ * is counting in or playing, not while idle.
+ */
+type Listener = (running: boolean) => void;
+
+const listeners = new Set<Listener>();
+let running = false;
+
+export const phraseRunBus = {
+    set(v: boolean): void {
+        if (v === running) return;
+        running = v;
+        listeners.forEach(l => l(v));
+    },
+    get(): boolean {
+        return running;
+    },
+    subscribe(l: Listener): () => void {
+        listeners.add(l);
+        return () => { listeners.delete(l); };
+    },
+};