refactor: extract _get_split_pattern into domain/split_pattern.py

- Extract unified split pattern logic to domain/split_pattern.py
- Add get_split_pattern() function with language and subtitle_mode support
- Remove duplicated logic from pyqt/conversion.py
- Update pyqt/conversion.py to use domain.split_pattern.get_split_pattern
- Add tests/test_split_pattern.py with 20 tests covering English, CJK, Spanish, French, and pattern structure

tests/test_split_pattern.py

@@ -0,0 +1,101 @@
+"""Tests for split pattern logic (3 identical copies in codebase)."""
+import os
+import sys
+sys.path.insert(0, os.path.abspath(os.path.join(os.path.dirname(__file__), "..")))
+
+import pytest
+
+from abogen.domain.split_pattern import get_split_pattern
+
+
+# --- English always returns \n ---
+
+class TestEnglish:
+    def test_english_sentence(self):
+        assert get_split_pattern("a", "Sentence") == "\n"
+
+    def test_english_sentence_comma(self):
+        assert get_split_pattern("a", "Sentence + Comma") == "\n"
+
+    def test_english_line(self):
+        assert get_split_pattern("a", "Line") == "\n"
+
+    def test_english_disabled(self):
+        assert get_split_pattern("a", "Disabled") == "\n"
+
+    def test_english_b(self):
+        assert get_split_pattern("b", "Sentence") == "\n"
+
+
+# --- CJK languages ---
+
+class TestCJK:
+    def test_chinese_disabled(self):
+        pattern = get_split_pattern("z", "Disabled")
+        assert pattern != "\n"
+        assert r"\n+" in pattern
+
+    def test_chinese_line(self):
+        pattern = get_split_pattern("z", "Line")
+        assert pattern != "\n"
+        assert r"\n+" in pattern
+
+    def test_chinese_sentence(self):
+        pattern = get_split_pattern("z", "Sentence")
+        assert r"\n+" in pattern
+
+    def test_chinese_sentence_comma(self):
+        pattern = get_split_pattern("z", "Sentence + Comma")
+        assert r"\n+" in pattern
+
+    def test_japanese_disabled(self):
+        pattern = get_split_pattern("j", "Disabled")
+        assert pattern != "\n"
+        assert r"\n+" in pattern
+
+    def test_japanese_sentence(self):
+        pattern = get_split_pattern("j", "Sentence")
+        assert r"\n+" in pattern
+
+
+# --- Other languages ---
+
+class TestOtherLanguages:
+    def test_spanish_sentence(self):
+        pattern = get_split_pattern("e", "Sentence")
+        assert r"\n+" in pattern
+
+    def test_spanish_line(self):
+        assert get_split_pattern("e", "Line") == "\n"
+
+    def test_spanish_disabled(self):
+        # canonical: \n+ for non-CJK Disabled
+        assert get_split_pattern("e", "Disabled") == r"\n+"
+
+    def test_french_sentence_comma(self):
+        pattern = get_split_pattern("f", "Sentence + Comma")
+        assert r"\n+" in pattern
+
+    def test_unknown_lang(self):
+        pattern = get_split_pattern("x", "Sentence")
+        assert r"\n+" in pattern
+
+
+# --- Pattern structure ---
+
+class TestPatternStructure:
+    def test_sentence_has_lookbehind(self):
+        pattern = get_split_pattern("e", "Sentence")
+        assert r"(?<=" in pattern
+
+    def test_sentence_comma_has_comma_chars(self):
+        pattern = get_split_pattern("e", "Sentence + Comma")
+        assert "," in pattern
+
+    def test_cjk_spacing_uses_star(self):
+        pattern = get_split_pattern("z", "Sentence")
+        assert r"\s*" in pattern
+
+    def test_non_cjk_spacing_uses_plus(self):
+        pattern = get_split_pattern("e", "Sentence")
+        assert r"\s+" in pattern