feat: Add 'call' support to improve 2-way audio experience (#2486)

Draws significant inspiration (and direct styling) from
https://github.com/dermotduffy/advanced-camera-card/pull/2447 . Thank
you @Maudfer !

BREAKING CHANGE:

The microphone condition previously bundled two unrelated signals —
whether a two-way-audio session was connected and whether the microphone
was muted. Connection state is now its own dedicated call condition, and
microphone is reserved purely for mute state. Configs are upgraded
automatically (the card rewrites affected conditions under overrides,
elements, and automations). If you maintain config by hand, convert as
follows:

If you only used connected:

# Before
```yaml
condition: microphone
connected: true
```

# After
```yaml
condition: call
call: true
```
If you used both connected and muted — they must be split into two
conditions, since they no longer live together:

# Before
```yaml
condition: microphone
connected: true
muted: false
```

# After
```yaml
condition: and
conditions:
  - condition: call
    call: true
  - condition: microphone
    muted: false
```

docs/usage/2-way-audio.md

@@ -17,8 +17,7 @@ challenging.
 
 - Only Frigate cameras are supported.
 - Only the `go2rtc` live provider is supported.
-- Only the `webrtc` mode supports 2-way audio:
-- Must have microphone menu button enabled:
+- Only the `webrtc` mode supports 2-way audio.
 
 If your setup supports 2-way audio but detection is intermittent on load:
 
@@ -37,24 +36,71 @@ cameras:
         - webrtc
       # Optional: For slower cameras increase timeout (default: 2)
       metadata_fetch_timeout_seconds: 10
-menu:
-  buttons:
-    microphone:
-      enabled: true
 ```
 
 ## Usage
 
+Two-way audio is driven by the **call** menu button (a phone icon). It is
+enabled by default and appears in the `live` view whenever the selected camera
+-- or one of its [dependencies](../configuration/cameras/README.md?id=dependencies)
+-- supports 2-way audio.
+
+- Tap the call button to start a call. An on-screen overlay appears with
+  controls to mute/unmute the microphone, mute/unmute the inbound audio, and end
+  the call. When more than one 2-way-audio camera is available the button
+  becomes a submenu with one entry per camera.
+- When a call starts the inbound audio is unmuted automatically, so the caller
+  can be heard immediately. The microphone stays muted by default
+  (push-to-talk) -- tap the microphone button in the overlay to speak. This is
+  configurable via [`live.microphone.auto_unmute`](../configuration/live.md?id=microphone)
+  and [`live.auto_unmute`](../configuration/live.md).
 - The camera will always load _without_ the microphone connected, unless the
-  [`always_connected`](../configuration/live.md?id=microphone) microphone option is
-  set to `true`.
-- To speak, hold-down the microphone menu button.
-  - On first press, this will reset the `webrtc` connection to include 2-way
-    audio unless [`always_connected`](../configuration/live.md?id=microphone) has
-    been used.
-  - Thereafter hold the microphone button down to unmute/speak, let go to
-    mute.
-- The video will automatically reset to remove the microphone after the number
-  of seconds specified by
-  [`disconnect_seconds`](../configuration/live.md?id=microphone) configuration have
-  elapsed since the last mute/unmute press.
+  [`always_connected`](../configuration/live.md?id=microphone) microphone option
+  is set to `true`. On the first call there may be a brief `webrtc` connection
+  reset to include 2-way audio.
+- While a call is in progress the card locks disruptive actions (camera and
+  substream changes, casting, reload, etc.) so an accidental tap, swipe, or
+  button press doesn't cut the call off. Set
+  [`live.controls.call.lock`](../configuration/live.md?id=call) to `false` to
+  disable this.
+- End the call with the overlay's end-call button. When the call ends the
+  microphone and inbound audio are muted again.
+- The video automatically resets to remove the microphone after the number of
+  seconds specified by [`disconnect_seconds`](../configuration/live.md?id=microphone)
+  have elapsed since the call ended.
+
+Calls can also be started and ended programmatically with the
+[`call_start`](../configuration/actions/custom/README.md?id=call_start) and
+[`call_end`](../configuration/actions/custom/README.md?id=call_end) actions --
+for example, from an [automation](../configuration/automations.md) that fires
+when a doorbell sensor triggers. The [`call` condition](../configuration/conditions.md?id=call)
+can be used to show or hide elements while a call is in progress.
+
+### Call lifecycle
+
+The diagram below traces a call from start to finish:
+
+![Call lifecycle sequence diagram](../images/call-sequence.svg ':size=600')
+
+## Talking with a single tap
+
+By default, two taps are needed to speak: the call button starts the call (so
+you can hear), then the microphone button in the call overlay unmutes your
+microphone (so you can be heard). This push-to-talk default keeps the microphone
+muted until you explicitly choose to speak.
+
+To collapse that to a single tap, unmute the microphone automatically when a
+call starts:
+
+```yaml
+live:
+  microphone:
+    auto_unmute: ['call']
+```
+
+The call button then behaves as a toggle -- one tap starts the call and opens
+the microphone, a second tap ends the call and closes it again. Note this also
+opens the microphone for calls started by an
+[automation](../configuration/automations.md); leave
+[`auto_unmute`](../configuration/live.md?id=microphone) empty (the default) to
+always start muted.