fix(scanner): route the audio-tag genre through the smart-genre pipeline

applyAudioTagFallbacks captured the ffprobe genre atom verbatim into
media_items.genre — no splitting, no shelf resolution, no cap. That raw
capture is what fed 100+-char Audible category blobs into the column
(the 2026-10 Crusader import/update failures).

The ABS sidecar path already has the correct doctrine (ab2a5568): a known
lexicon shelf wins the genre column, everything else is tags-only. Give
the tag fallback the same treatment — splitGenreCandidates +
pickSmartGenre for the column, split candidates appended to tags
(NormalizeTags dedups). Demoted genres like "Audiobook" stop masquerading
as a shelf, and an unknown blob can no longer manufacture an overflowing
value at all.

Fixtures pin the new behavior: the real 111-char Crusader blob stays out
of the column entirely and lands as six separate tags; a shelf-carrying
blob still wins the column; the previously-pinned verbatim "Audiobook"
expectation is updated to the demoted (tags-only) contract.

internal/services/media_scanner_audio.go

@@ -30,6 +30,8 @@ import (
 	"strconv"
 	"strings"
 	"time"
+
+	"bookhoard/internal/utils"
 )
 
 // AudioChapter is the uniform chapter entry for every audiobook file model.
@@ -394,7 +396,8 @@ func marshalAudioMetadata(payload *AudioMetadataPayload) []byte {
 //	----:com.apple.iTunes:SUBTITLE       → joined into the title
 //	  ("Title: Subtitle"), mirroring the ABS sidecar path
 //	----:com.apple.iTunes:ASIN / ABRIDGED → asin / abridged flag
-//	date → publish date; genre → genre
+//	date → publish date; genre → smart-genre (shelf-or-empty column,
+//	split candidates to tags — see pickSmartGenre)
 //
 // Abridged is the one field where an explicit sidecar false must not be
 // overridden by a tag — the payload pointer marks sidecar presence.
@@ -472,7 +475,21 @@ func applyAudioTagFallbacks(metadata *MediaMetadata, report *ffprobeReport) {
 		}
 	}
 	if metadata.Genre == "" {
-		metadata.Genre = report.tag("genre")
+		// Same doctrine as the ABS sidecar path (ab2a5568): the raw file
+		// atom is a comma-joined category blob ("Politicians, Presidents &
+		// Heads of State, United States, ..." — Audible ladders, often past
+		// 100 chars). Shelf-or-empty wins the genre column; every split
+		// candidate lands in tags. No shelf match → the column stays empty
+		// and the blob is tags-only, never a VARCHAR-overflowing INSERT.
+		if genreTag := report.tag("genre"); genreTag != "" {
+			genre, all := pickSmartGenre([]string{genreTag})
+			if genre != "" {
+				metadata.Genre = genre
+			}
+			if len(all) > 0 {
+				metadata.Tags = utils.NormalizeTags(append(metadata.Tags, all...))
+			}
+		}
 	}
 }