feat(f8): CJK-safe search text normalization + matching

normalizeForIndex (lowercase + collapse whitespace runs incl. hard PDF/OCR
newlines + trim) and matchesNormalized so a query matches across the line breaks
in raw extracted text. Deliberately NO word-tokenization: Chinese has no
inter-word spaces, so substring match over normalized text is correct for both
Latin and CJK (段/word segmentation belongs in the DB FTS tokenizer). Verified
on CJK inputs (你好/笔记应用).

flutter analyze lib/editor clean; 181/181 tests (+9).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

test/search_text_test.dart

@@ -0,0 +1,51 @@
+// Tests for CJK-safe search text normalization + matching (F8).
+
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:badnote/editor/search/search_text.dart';
+
+void main() {
+  group('normalizeForIndex', () {
+    test('lowercases and collapses whitespace runs to single spaces', () {
+      expect(normalizeForIndex('Hello   World'), 'hello world');
+      expect(normalizeForIndex('a\t b\n\nc'), 'a b c');
+    });
+
+    test('trims leading/trailing whitespace', () {
+      expect(normalizeForIndex('  padded  '), 'padded');
+    });
+
+    test('collapses hard newlines from PDF/OCR mid-sentence', () {
+      expect(normalizeForIndex('hello\nworld'), 'hello world');
+    });
+
+    test('leaves CJK intact (no tokenization/mangling)', () {
+      expect(normalizeForIndex('你好  世界'), '你好 世界');
+      expect(normalizeForIndex('笔记\n应用'), '笔记 应用');
+    });
+  });
+
+  group('matchesNormalized', () {
+    test('matches across a line break in the source', () {
+      expect(matchesNormalized('hello\nworld', 'hello world'), isTrue);
+    });
+
+    test('is case-insensitive', () {
+      expect(matchesNormalized('The Quick Fox', 'quick'), isTrue);
+    });
+
+    test('CJK substring match works', () {
+      expect(matchesNormalized('这是一个笔记应用', '笔记'), isTrue);
+      expect(matchesNormalized('这是一个笔记\n应用', '笔记 应用'), isTrue);
+    });
+
+    test('empty query never matches', () {
+      expect(matchesNormalized('anything', ''), isFalse);
+      expect(matchesNormalized('anything', '   '), isFalse);
+    });
+
+    test('non-match returns false', () {
+      expect(matchesNormalized('hello world', 'zzz'), isFalse);
+    });
+  });
+}