feat(dictation): show live mic level while recording

Add a pulsing halo behind the stop button that scales with the
microphone input level, giving real-time feedback that recording is
active and the mic is picking up sound.

- use-dictation: meter the captured MediaStream via AudioContext +
  AnalyserNode (analyser only, never connected to destination), compute
  a smoothed RMS audioLevel (0..1) in a requestAnimationFrame loop, and
  tear the meter down on every recording-end path (stop/cancel/auto-stop/
  unmount); meter failure is non-fatal to recording
- mic-button: render a translucent red halo whose scale follows
  audioLevel; honor prefers-reduced-motion with a static halo
- stop(): recover and release resources when no live recorder remains
- fix unhandled rejection from AudioContext.resume()

apps/client/src/features/dictation/components/mic-button.module.css

@@ -0,0 +1,22 @@
+.recordingWrap {
+  position: relative;
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+}
+
+/* Translucent red halo that sits behind the stop button and scales with the
+   live microphone level (scale set inline from audioLevel). */
+.pulse {
+  position: absolute;
+  inset: 0;
+  border-radius: 50%;
+  background-color: var(--mantine-color-red-5);
+  opacity: 0.35;
+  transform-origin: center;
+  transform: scale(1);
+  transition: transform 90ms linear;
+  pointer-events: none;
+  will-change: transform;
+  z-index: 0;
+}