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.

docs/CURRENT-STATE.md

@@ -2955,9 +2955,10 @@ down | auth-failed` (plus the unchanged `missing-key`/`unsupported`) with
 >   take over under the Cockpit cap of 60. Loading/capped contacts remain 2D,
 >   out-of-range contacts use rotation-free dots, and exit restores map treatment.
 >   Its Radio popover exposes compact power,
->   transport, station, and volume controls. Cockpit Previous/Next preserves
->   selection, autoplay, and broadcaster fallback audio without starting the
->   map-view station flights that compete with the first-person camera. These
+>   transport, station, and volume controls. Cockpit Previous/Next changes the
+>   selection without starting the map-view station flights that compete with
+>   the first-person camera; like the Context Previous/Next buttons, it plays
+>   (with broadcaster fallback) only while a stream is already active. These
 >   are a Cockpit-only accordion:
 >   each static header uses the left accordion's label and divider with a dedicated
 >   directional-chevron disclosure button and no full-row hover treatment. Only one
@@ -4760,7 +4761,9 @@ before the later control succeeds, only its playback handoff is suppressed; its
 result reads enabled state from the manager and audio state from the Radio
 module. Voice Pause is a playback-only no-op while the layer is disabled; it
 never enables Radio and reports a fulfilled-false pause as failure. A
-newer-response or user-origin Stop still cancels stale handoff work.
+newer-response or user-origin Stop still cancels stale handoff work, as do a
+user Pause, a user Previous/Next that only selects another station, and a tuner
+release onto a station the directory no longer has.
 Only a newer user turn or session teardown aborts the complete active-tool set.
 A cancelled turn cannot publish a late Radio playback request. Dedicated Radio
 controls and generic layer-visibility commands both forward cancellation.