feat(dates): pre-cutover audit utility for the filename date class (#117)

One-shot, operator-run, strictly read-only utility that lists every
filename-class file with its stored date/source and the date/source/
offset-source the re-based resolver would assign it — the human
spot-check that gates the production backfill drain (#118).

- src/filename_audit.rs: StoredDate/AuditRow/SkippedLibrary; walk +
  PathExcluder (depth-0 guarded) + match_filename_date -> one
  resolve_dates_batch pass with EMPTY priors (mirrors the drain
  exactly); disabled and probe-stale libraries reported as skipped,
  never partially processed; output stable-sorted by (library, path).
- src/bin/filename_audit.rs: operator binary (dotenv, DATABASE_URL,
  EXCLUDED_DIRS, libraries::load_all, format_report).
- src/memories.rs: match_filename_date canonical matcher returning
  FilenameMatch { pattern, date }; extract_date_from_filename is now
  a thin wrapper (byte-for-byte behavior-preserving, verified by
  review).

4 audit tests (inversion + utc_direct + exclusions, offline/disabled
skip, stable sort, report determinism incl. no debug quotes) + 2
matcher tests. 645 lib + 718 integration pass; clippy/fmt clean.
Standards review applied: {:?}->{}, depth-0 walk guard, dead
per-file exclude check removed, unused Default derive removed,
pattern column widened, doc comment reworded.

src/lib.rs

@@ -21,6 +21,7 @@ pub mod face_watch;
 pub mod faces;
 pub mod file_scan;
 pub mod file_types;
+pub mod filename_audit;
 pub mod files;
 pub mod geo;
 pub mod libraries;