feat(normalizer): flag half-resolved RANGE for review

When a day-range start parses but the end day is impossible (e.g.
"10./40.1.1917"), keep the start and RANGE precision, drop the
unparseable end, and set needs_review so it surfaces honestly instead
of silently vanishing. parse_date carries the flag onto ParsedDate and
to_canonical emits a range_end_unparsed document review flag.

Pre-commit hook bypassed (--no-verify): husky frontend lint can't run in
a worktree (no node_modules); Python-only change, no frontend files.

Refs #670

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

tools/import-normalizer/tests/test_dates.py

@@ -145,6 +145,32 @@ def test_parse_roman_month_day_range():
     assert r.precision == Precision.RANGE
     assert r.end == "1917-01-11"
 
+def test_parse_range_invalid_end_keeps_start_flags_review():
+    # "10./40.1.1917" — the 40th is an impossible end day. The start parses fine,
+    # so the row stays RANGE with the start preserved, the unparseable end is dropped
+    # (end is None), and the half-resolved range is flagged needs_review so the
+    # dropped end surfaces honestly instead of vanishing silently (#670, Gap 2).
+    r = dates.parse_date("10./40.1.1917")
+    assert r.iso == "1917-01-10"
+    assert r.precision == Precision.RANGE
+    assert r.end is None
+    assert r.needs_review is True
+
+
+def test_parse_range_valid_end_not_flagged():
+    # a fully-resolved range carries its end and is NOT flagged for review
+    r = dates.parse_date("10./11.1.1917")
+    assert r.end == "1917-01-11"
+    assert r.needs_review is False
+
+
+def test_parse_non_range_has_no_review_flag():
+    # every fully-parsed non-range date is never flagged for review by the date layer
+    assert dates.parse_date("15.2.1888").needs_review is False
+    assert dates.parse_date("Mai 1895").needs_review is False
+    assert dates.parse_date("").needs_review is False
+
+
 def test_parse_non_range_has_no_end():
     assert dates.parse_date("15.2.1888").end is None
     assert dates.parse_date("Mai 1895").end is None