camera: mirror preview only, not capture (telegram fidelity)

Drop isVideoMirrored on the AVCaptureVideoDataOutput connection — the
data output feeds both the preview texture AND the recorder, so any
mirror set there ended up baked into the recorded MP4. Recorded video
+ captured JPEG now carry the raw sensor feed ("as others see you"),
matching telegram-iOS and the stock iOS Camera app default.

The selfie preview is mirrored inside UxCameraPreview itself
(Transform.flip(flipX: true) around the Texture when
description.lens == front) — the analog of telegram's
CameraPreviewView.mirroring CALayer transform. Consumers
(CameraThumb, etc.) don't need to know which lens is active.

lib/src/camera/camera_preview.dart

@@ -1,6 +1,6 @@
 import 'package:flutter/widgets.dart';
 
-import 'camera.dart' show UxCameraController, UxCameraValue;
+import 'camera.dart' show UxCameraController, UxCameraLens, UxCameraValue;
 
 /// Renders the live preview for [controller] into a [Texture]. Sizes
 /// itself to the parent — wrap in `AspectRatio` / `FittedBox` / `Hero`
@@ -10,6 +10,11 @@ import 'camera.dart' show UxCameraController, UxCameraValue;
 /// transparent placeholder. The widget rebuilds on every
 /// `UxCameraValue` change, so once the native session starts
 /// producing frames the texture appears automatically.
+///
+/// Front-camera preview is auto-mirrored here (the analog of
+/// telegram-iOS's `CameraPreviewView.mirroring` property), so the
+/// recorded MP4 + captured JPEG carry the raw sensor feed while the
+/// on-screen preview still reads as a natural mirror to the user.
 class UxCameraPreview extends StatelessWidget {
   const UxCameraPreview({super.key, required this.controller});
 
@@ -19,10 +24,14 @@ class UxCameraPreview extends StatelessWidget {
   Widget build(BuildContext context) {
     return ValueListenableBuilder<UxCameraValue>(
       valueListenable: controller,
-      builder: (context, _, __) {
+      builder: (context, value, _) {
         final id = controller.textureId;
-        if (id == null) return const SizedBox.expand();
-        return Texture(textureId: id);
+        if (id == null) return SizedBox.expand();
+        final mirror = value.description.lens == UxCameraLens.front;
+        final texture = Texture(textureId: id);
+        return mirror
+            ? Transform.flip(flipX: true, child: texture)
+            : texture;
       },
     );
   }