fix: Release the microphone to the browser when a call ends (#2685)

The microphone is connected when a call needs it and released the moment
that
call ends, so the browser stops reporting it as in use at hangup rather
than
`disconnect_seconds` later.

Existing configurations are migrated automatically by the visual editor.

 - Closes: #2681 

BREAKING CHANGE: `live.microphone.disconnect_seconds` is removed. The
microphone is released when a call ends, so there is no idle countdown
to
configure. Use `live.microphone.always_connected` to hold it open
instead.

BREAKING CHANGE: The `microphone_connect` and `microphone_disconnect`
actions
are removed. The card owns the microphone lifecycle; `microphone_mute`
and
`microphone_unmute` remain.

BREAKING CHANGE: `call` is removed from `live.microphone.auto_mute`,
whose
default is now `[]`. The microphone is muted when a call ends regardless
of
this option.

BREAKING CHANGE: `microphone_unmute` has no effect outside a call.
Nothing
carries the audio at any other time, so the request is ignored rather
than
opening the microphone.

src/config/schema/live.ts

@@ -25,9 +25,8 @@ import { transitionEffectConfigSchema } from './common/transition-effect';
 
 const microphoneConfigDefault = {
   always_connected: false,
-  auto_mute: ['call' as const],
+  auto_mute: [],
   auto_unmute: [],
-  disconnect_seconds: 90,
   mute_after_microphone_mute_seconds: 60,
 };
 
@@ -80,10 +79,6 @@ const microphoneConfigSchema = z
       .enum(MICROPHONE_UNMUTE_CONDITIONS)
       .array()
       .default(microphoneConfigDefault.auto_unmute),
-    disconnect_seconds: z
-      .number()
-      .min(0)
-      .default(microphoneConfigDefault.disconnect_seconds),
     mute_after_microphone_mute_seconds: z
       .number()
       .min(0)