fix(voice): keep chat's view across a provider switch and clear stale errors

Switching AI Provider in Settings opened from chat rebuilt the voice
control, so Settings fell back to voice and the dock went idle, widening
the wings. The switch now carries chat's Settings, or chat itself, to the
new provider as it already carries the input mode; the conversation still
starts fresh and focus stays on the provider choice.

After a voice error, opening chat or closing the voice panel left the dock
red on ERROR, because both stopped only an active session. They now also
end a session left in error, which returns the dock to idle.

docs/CURRENT-STATE.md

@@ -766,9 +766,12 @@ each side, and the empty Voice Preview suggests things to say until voice
 starts. Settings opened from chat keep chat's frame and show the shared AI
 provider, the quick-commands option and then the voice preferences (Voice
 Preview, inactivity timeout and model tier), so they stay in reach while
-Preview is off, with Back to chat; voice Settings show Back to voice. Escape steps back from either Settings view, closes Voice
+Preview is off, with Back to chat; voice Settings show Back to voice. Switching
+AI Provider keeps that view: chat's Settings, or chat itself, stay as they were
+for the new provider. Escape steps back from either Settings view, closes Voice
 Preview, and does nothing in chat. Closing chat ends a typed session, and the
-voice panel's close turns voice off. Asking the assistant from chat to open
+voice panel's close turns voice off. Opening chat or closing the voice panel
+also clears a voice error left on the dock. Asking the assistant from chat to open
 Voice Settings or Voice Preview puts chat away, minimized or not, and shows the
 voice panel; the typed conversation and its running reply carry on, and the
 chat button brings them back.