Fixes a bug where ISO-formatted dates (e.g. '2023-01 – 2025-03') in the
period field were split incorrectly. The old code replaced the en-dash with
a hyphen first, then split on the first hyphen, causing dates like '2023-01'
to be split into '2023' and '01' instead of the expected start/end pair.
The fix splits on the dash/dash separator *before* normalizing to plain
hyphens, ensuring round-trip conversion of dates with embedded hyphens.
Adds two regression tests:
- test_profile_to_library_period_split_iso_dates: verifies en-dash separation
- test_profile_to_library_period_split_em_dash: verifies em-dash separation
Pure transform functions (no LLM, no DB) bridging the two resume
representations: library struct_json ↔ ResumePayload content fields.
Exports library_to_profile_content, profile_to_library,
make_auto_backup_name, blank_fields_on_import. 22 tests, all passing.
