Add a microphone level meter

- Draws the level as lit bars, and each failure state as its own message with a
  next action rather than as a meter that has stopped.
- A bar and the space beside it keep one size wherever the meter is drawn; what
  the width decides is how many bars there are. Bars spread to fill would be a
  different shape in every place, and would close into one block where the space
  ran short.
- Announces the level on a fixed scale, so it does not rest on hue or on how
  many bars happened to fit.
- The hook is a bridge and nothing more: the capture belongs to the state layer.
- The capture is held by a component of its own, so a level that does change
  redraws the meter rather than whatever is rendered beside it. A level arrives
  many times a second; held by the menu it would reconcile every device row on
  the way to the bars. A test counts those renders, because nothing else would
  notice the hook moving back.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

locales/en/app.json

@@ -163,6 +163,12 @@
   "login_auth_links_prompt": "Not registered yet?",
   "login_subheading": "To continue to Element",
   "login_title": "Login",
+  "microphone_level": {
+    "label": "Microphone level",
+    "no_device": "No microphone found. Connect one, then try again.",
+    "permission_denied": "Element Call cannot use your microphone. Allow access in your browser settings.",
+    "value": "{{level}} of {{max}}"
+  },
   "microphone_off": "Microphone off",
   "microphone_on": "Microphone on",
   "mute_microphone_button_label": "Mute microphone",
@@ -215,11 +221,14 @@
       "activating": "Activating…",
       "camera": "Camera",
       "camera_numbered": "Camera {{n}}",
+      "camera_source": "Camera Source",
       "change_device_button": "Change audio device",
       "default": "Default",
       "default_named": "Default <2>({{name}})</2>",
+      "default_named_plain": "Default ({{name}})",
       "handset": "Handset",
       "loudspeaker": "Loudspeaker",
+      "mic_source": "Mic Source",
       "microphone": "Microphone",
       "microphone_numbered": "Microphone {{n}}",
       "speaker": "Speaker",