DB now source of truth for folder -> Serie resolution.
Changes:
- AnimeSeriesService.get_by_folder(): new async lookup by folder name
- SerieScanner.__read_data_from_file(): query DB first, then provider callback, then legacy key file (temporary, removed v3.0.0)
- Serie: reconstruct from DB record with episode dict
- Key file: warn on use, scheduled removal v3.0.0
Add unit tests for DB hit/miss/callback/fallback edge cases
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
