Draw the microphone level without re-rendering

- The level state carries a Behavior, so the state changes only when its kind
  does.
- The meter renders its bars once and an effect draws the level into them.
- The render-counting test now counts every commit, and asserts none while the
  level moves.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/components/useMicrophoneLevel.test.tsx

@@ -35,6 +35,7 @@ describe("useMicrophoneLevel", () => {
     rerender({ id: "mic2" });
 
     // No level carried over from the previous device.
-    expect(result.current).toEqual({ type: "level", level: 0 });
+    const state = result.current;
+    expect(state.type === "level" ? state.level.value : state.type).toBe(0);
   });
 });