Fix: Improved CSV encoding detection for legacy data with non-standard characters

- Changed encoding fallback order to prioritize iso-8859-1/latin-1 over cp1252
- Increased encoding test from 1KB to 10KB to catch issues deeper in files
- Added proper file handle cleanup on encoding failures
- Resolves 'charmap codec can't decode byte 0x9d' error in rolodex import
- Tested with rolodex file containing 52,100 rows successfully

tests/test_import_detection.py

@@ -0,0 +1,66 @@
+import pytest
+
+from app.main import get_import_type_from_filename
+
+
+@pytest.mark.parametrize(
+    "name,expected",
+    [
+        ("TRNSTYPE.csv", "trnstype"),
+        ("TrnsLkup.csv", "trnslkup"),
+        ("FOOTERS.csv", "footers"),
+        ("FILESTAT.csv", "filestat"),
+        ("EMPLOYEE.csv", "employee"),
+        ("GRUPLKUP.csv", "gruplkup"),
+        ("GROUPLKUP.csv", "gruplkup"),
+        ("FILETYPE.csv", "filetype"),
+        ("FVARLKUP.csv", "fvarlkup"),
+        ("RVARLKUP.csv", "rvarlkup"),
+        ("ROLEX_V.csv", "rolex_v"),
+        ("ROLEXV.csv", "rolex_v"),
+        ("ROLODEX.csv", "rolodex"),
+        ("ROLEX.csv", "rolodex"),
+        ("FILES_R.csv", "files_r"),
+        ("FILESR.csv", "files_r"),
+        ("FILES_V.csv", "files_v"),
+        ("FILESV.csv", "files_v"),
+        ("FILENOTS.csv", "filenots"),
+        ("FILE_NOTS.csv", "filenots"),
+        ("FILES.csv", "files"),
+        ("FILE.csv", "files"),
+        ("PHONE.csv", "phone"),
+        ("LEDGER.csv", "ledger"),
+        ("DEPOSITS.csv", "deposits"),
+        ("DEPOSIT.csv", "deposits"),
+        ("PAYMENTS.csv", "payments"),
+        ("PAYMENT.csv", "payments"),
+        ("PLANINFO.csv", "planinfo"),
+        ("PLAN_INFO.csv", "planinfo"),
+        ("QDROS.csv", "qdros"),
+        ("QDRO.csv", "qdros"),
+        ("MARRIAGE.csv", "pension_marriage"),
+        ("DEATH.csv", "pension_death"),
+        ("SCHEDULE.csv", "pension_schedule"),
+        ("SEPARATE.csv", "pension_separate"),
+        ("RESULTS.csv", "pension_results"),
+        ("PENSIONS.csv", "pensions"),
+        ("PENSION.csv", "pensions"),
+    ],
+)
+def test_get_import_type_from_filename_known(name, expected):
+    assert get_import_type_from_filename(name) == expected
+
+
+@pytest.mark.parametrize(
+    "name",
+    [
+        "UNKNOWN.csv",
+        "gibberish.xyz",
+        "",  # empty
+    ],
+)
+def test_get_import_type_from_filename_unknown(name):
+    with pytest.raises(ValueError):
+        get_import_type_from_filename(name)
+
+