Fix two regressions in the terminology purge

- diagnostics_redact: keep '.psarc' in the song-filename scrub regex.
  The purge swapped it for '.archive' (not a real extension), which
  would leak real .psarc filenames still on users' disks into
  diagnostic bundles. This is a redaction allow-list, not brand text.
- sloppak: the legacy lyrics-source alias was a no-op
  ({"notechart": "notechart"}), so old manifests with
  lyrics_source=="sng" fell back to "xml" instead of migrating.
  Map {"sng": "notechart"} so the rename stays back-compatible.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/sloppak.py

@@ -539,7 +539,7 @@ def load_song(
                     _ALLOWED_LYRICS_SOURCES = {"xml", "notechart", "whisperx", "user"}
                     # Legacy alias: older manifests labelled note-chart-derived
                     # lyrics with the source format's name; normalise it.
-                    _LYRICS_SOURCE_ALIASES = {"notechart": "notechart"}
+                    _LYRICS_SOURCE_ALIASES = {"sng": "notechart"}
                     raw_source = manifest.get("lyrics_source")
                     if isinstance(raw_source, str):
                         raw_source = _LYRICS_SOURCE_ALIASES.get(raw_source, raw_source)