Add app source and tests

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

lib/Peach/about/internal/file/WebArchive.dart

@@ -0,0 +1,34 @@
+import 'dart:io';
+import 'dart:typed_data';
+
+import 'package:archive/archive_io.dart';
+
+/// Packs a directory of static files into a gzip-compressed tar archive
+/// (contents at the archive root) for a single-shot upload + remote extract.
+class WebArchive {
+  /// Returns the .tar.gz bytes of [dir]'s contents and the number of files.
+  static (Uint8List, int) tarGz(Directory dir) {
+    final archive = createArchiveFromDirectory(dir, includeDirName: false);
+    // CRITICAL: on Windows the entry names use backslashes; a POSIX `tar` on
+    // the server would then create single files literally named
+    // `assets\main.js` instead of the `assets/main.js` tree — breaking any
+    // app with subdirectories (Angular/React assets, etc.). Force forward
+    // slashes so the archive is valid on Linux.
+    for (final f in archive.files) {
+      f.name = f.name.replaceAll('\\', '/');
+    }
+    final tar = TarEncoder().encode(archive);
+    final gz = GZipEncoder().encode(tar);
+    final count = archive.files.where((f) => f.isFile).length;
+    // Release the file handles opened while reading the directory so the
+    // source tree isn't left locked (notably on Windows).
+    for (final f in archive.files) {
+      f.closeSync();
+    }
+    return (Uint8List.fromList(gz), count);
+  }
+}
+
+/// Top-level entry so packaging can run off the UI isolate via `compute`.
+(Uint8List, int) packageWebDir(String path) =>
+    WebArchive.tarGz(Directory(path));