feat(radio): answer the RTL-SDR card through the radio store

SdrCard calls LocalSdrControls through radio store actions instead of
DOM listeners, and renders its gain options from the receiver's own
R820T gain steps with page-language labels. The display and radio
stores share one owner list (createOwners): the newest connected owner
with an action answers it.

docs/VUE-MIGRATION.md

@@ -147,7 +147,8 @@ a feature supplying only its accent.
    Context and Radio (in progress: `RadioPanel` renders the directory row,
    station card, transport, volume and playback line from the `gev-radio`
    store that RadioControls publishes to, and `SdrCard` the local RTL-SDR
-   card that LocalSdrControls publishes beside it; fields a person edits take
+   card that LocalSdrControls publishes beside it and answers through the
+   store's `connect`/`act` (the shared `createOwners()`); fields a person edits take
    their value through `v-field-value`, which never writes a focused field;
    `RadioTuner` renders the directory tuner, where RadioControls keeps the
    drag and its slot and publishes the band, readouts, slider and needle,