Keep Radio playback state consistent after a silent Next

Review follow-ups for HAL-722. A Next or Previous that only selects a
station now leaves nothing of the previous stream behind:

- Selecting another station without playing stops a paused or failed
  stream, so the panel, Stop, voice summaries and the audio element agree
  on "stopped". A fallback the caller armed for the new selection is kept.
- A silent UI step arms no broadcaster fallback, and a user Play of the
  selected station drops one left by a cancelled voice step. Voice steps
  pass `fallback: true` because voice starts the prepared playback later.
- A user step to another station emits a `select` playback control, and
  the realtime voice handoff treats it like Pause and Stop.
- A tuner release onto a station the directory no longer has stops the
  stream the drag paused, publishing one state with the gesture's origin,
  so the button reads PLAY and a voice handoff is cancelled.
- The transport buttons offer Pause while a stream connects, matching
  what a click does.
- The privacy note names every action that connects to a broadcaster
  (play, finishing tuning, choosing a station on the globe) in all
  locales.

The Next/Previous layer tests live in src/data/radioNextState.test.mjs.

changelog.d/1474-radio-next-no-autoplay.md

@@ -1,3 +1,5 @@
 - Radio Next and Previous no longer start a broadcaster stream before Play is
   pressed: they only select a station, and once a stream is playing it follows
-  the new station (gekh, #1474).
+  the new station. Stepping away from a paused or failed stream releases it, the
+  Play button offers Pause while a stream connects, and the privacy note names
+  every action that connects to a broadcaster (gekh, #1474).