Add ability to send images over lora

lib/helpers/image_send_flow.dart

@@ -0,0 +1,78 @@
+import 'dart:io';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+import 'package:image_picker/image_picker.dart';
+
+import '../l10n/l10n.dart';
+import '../widgets/image_send_codec_binding.dart';
+import '../widgets/image_send_preview_sheet.dart';
+
+/// Shared "attach an image" flow, used by both the direct-message and channel
+/// chat screens so the two surfaces cannot drift apart.
+///
+/// Picks a photo, then shows [ImageSendPreviewSheet] so the user sees the
+/// packet count and airtime *before* committing to a send that may occupy the
+/// channel for seconds. Returns null if the user backed out at either step.
+///
+/// The caller owns the actual transmission: this only produces the payload.
+Future<ImageSendPreviewResult?> pickAndPreviewImage({
+  required BuildContext context,
+  required ImageSendCodec codec,
+  ImagePicker? picker,
+}) async {
+  final XFile? picked;
+  try {
+    picked = await (picker ?? ImagePicker()).pickImage(
+      source: ImageSource.gallery,
+      // The codec centre-crops to 512x512 anyway, so there is nothing to gain
+      // from decoding a 12 MP original -- but stay well above 512 so the crop
+      // still has detail to work with.
+      maxWidth: 2048,
+      maxHeight: 2048,
+    );
+  } on Exception catch (e) {
+    debugPrint('image pick failed: $e');
+    if (context.mounted) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text(context.l10n.chat_imagePickFailed)),
+      );
+    }
+    return null;
+  }
+
+  if (picked == null) return null; // user cancelled the picker
+
+  final Uint8List bytes;
+  int originalBytes;
+  try {
+    bytes = await picked.readAsBytes();
+    originalBytes = bytes.length;
+    if (!kIsWeb) {
+      // length() is the on-disk size, which is what we want to show against the
+      // transmitted size; fall back to the in-memory length if it fails.
+      try {
+        originalBytes = await File(picked.path).length();
+      } on FileSystemException {
+        // keep the in-memory length
+      }
+    }
+  } on Exception catch (e) {
+    debugPrint('image read failed: $e');
+    if (context.mounted) {
+      ScaffoldMessenger.of(context).showSnackBar(
+        SnackBar(content: Text(context.l10n.chat_imagePickFailed)),
+      );
+    }
+    return null;
+  }
+
+  if (!context.mounted) return null;
+
+  return showImageSendPreviewSheet(
+    context: context,
+    imageBytes: bytes,
+    originalFileBytes: originalBytes,
+    codec: codec,
+  );
+}