refactor(anaf): remove dead code in sanitize_cui, fix empty test

Remove unreachable OCR-skip fallback (raw_bare can't be all-digits
if strip_ro_prefix changed it via OCR fix). Add real test for the
checksum result==10→0 branch using CUI 14186770.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

api/tests/test_cui_validation.py

@@ -148,15 +148,14 @@ class TestValidateCuiChecksum:
         assert validate_cui_checksum("1") is False
 
     def test_checksum_result_10_becomes_0(self):
-        """When (sum*10)%11 == 10, check digit should be 0."""
-        # Build a CUI where the algorithm yields 10
-        # Body 12345678 → pad to 9: 012345678
-        # 0*7+1*5+2*3+3*2+4*1+5*7+6*5+7*3+8*2 = 0+5+6+6+4+35+30+21+16 = 123
-        # 123*10=1230, 1230%11 = 111*11=1221, remainder=9 → check=9 → not 10
-        # Let's just verify a known CUI ending in 0 works
-        # CUI 46628322 from data: check=2, not 0. Skip this specific edge case test
-        # and just verify the code path exists
-        pass
+        """When (sum*10)%11 == 10, check digit should be 0.
+
+        CUI 14186770: body=1418677, padded=001418677,
+        sum=0+0+3+8+1+42+35+21+14=124, 1240%11=10 → check=0.
+        """
+        assert validate_cui_checksum("14186770") is True
+        # Wrong check digit for same body
+        assert validate_cui_checksum("14186771") is False
 
 
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