feat: add CodeParser for barcode classification per PRD §4

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/services/code_parser.dart

@@ -0,0 +1,39 @@
+// lib/services/code_parser.dart
+class CodeParser {
+  static final _zongpaiRegex = RegExp(
+    r'^\d{2}(B|C|T)\d+$|^\d{2}(BW|CW)\d{4}$',
+  );
+  static final _locationRegex = RegExp(
+    r'^[A-Z0-9]+-[A-Z0-9]+-[A-Z0-9]+$',
+  );
+  static final _transitRegex = RegExp(
+    r'^TRANS-',
+  );
+
+  static ParseResult parse(String code) {
+    if (code.isEmpty) {
+      return ParseResult(type: CodeType.invalid, value: code);
+    }
+    if (_transitRegex.hasMatch(code)) {
+      return ParseResult(type: CodeType.locationTransit, value: code);
+    }
+    if (_zongpaiRegex.hasMatch(code)) {
+      return ParseResult(type: CodeType.zongpaiNo, value: code);
+    }
+    if (_locationRegex.hasMatch(code)) {
+      return ParseResult(type: CodeType.locationNormal, value: code);
+    }
+    return ParseResult(type: CodeType.invalid, value: code);
+  }
+
+  static bool isLocation(CodeType type) =>
+      type == CodeType.locationNormal || type == CodeType.locationTransit;
+}
+
+enum CodeType { zongpaiNo, locationNormal, locationTransit, invalid }
+
+class ParseResult {
+  final CodeType type;
+  final String value;
+  ParseResult({required this.type, required this.value});
+}