feat(normalizer): year expansion century rule

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/import-normalizer/tests/test_dates.py

@@ -24,3 +24,15 @@ def test_resolve_season():
 
 def test_resolve_unknown_token_returns_none():
     assert dates.resolve_feast_or_season("Freitag", 1919) is None
+
+def test_expand_year():
+    assert dates.expand_year("1888") == 1888
+    assert dates.expand_year("889") == 1889      # 3-digit -> 1DDD
+    assert dates.expand_year("923") == 1923
+    assert dates.expand_year("08") == 1908       # 00..57 -> 19xx
+    assert dates.expand_year("17") == 1917
+    assert dates.expand_year("57") == 1957
+    assert dates.expand_year("73") == 1873       # 73..99 -> 18xx
+    assert dates.expand_year("99") == 1899
+    assert dates.expand_year("65") is None       # 58..72 ambiguous
+    assert dates.expand_year("x") is None