Fixed typo in the audio settings UI of the example app (#942)

Changes:

Updated text labels to "Microphone"

Updated dropdown placeholder

Why:
Improves clarity and professionalism in the example UI.

Testing:
Manually tested on Android emulator + physical device.

---------

Co-authored-by: Hiroshi Horie <548776+hiroshihorie@users.noreply.github.com>

Author: mechtech-mind

.changes/prejoin-microphone-label

@@ -0,0 +1 @@
+patch type="fixed" "Fix microphone label typo in example app prejoin audio settings"

example/lib/pages/prejoin.dart

@@ -429,7 +429,7 @@ class _PreJoinPageState extends State<PreJoinPage> {
                   child: Row(
                     mainAxisAlignment: MainAxisAlignment.spaceBetween,
                     children: [
-                      const Text('Micriphone:'),
+                      const Text('Microphone:'),
                       Switch(
                         value: _enableAudio,
                         onChanged: (value) => _setEnableAudio(value),
@@ -444,7 +444,7 @@ class _PreJoinPageState extends State<PreJoinPage> {
                       isExpanded: true,
                       disabledHint: const Text('Disable Microphone'),
                       hint: const Text(
-                        'Select Micriphone',
+                        'Select Microphone',
                       ),
                       items: _enableAudio
                           ? _audioInputs