fix: populate canonical_name and stop writing generated normalized_name

Three separate insert paths made a fresh Postgres volume unusable. The live
database only works because its volume predates the constraints.

  - scanner.service.resolveOrCreateArtist inserted only (name), but
    schema.sql declares canonical_name NOT NULL with no default. Every
    artist insert failed, and processFile swallows per-file errors, so a
    scan reported success with 0 tracks and a permanently empty library.
  - enrichment.service inserted explicitly into artists.normalized_name,
    which is GENERATED ALWAYS AS (normalize_artist(name)) STORED:
    "cannot insert a non-DEFAULT value into column" (428C9). All
    enrichment artist creation failed on a fresh volume.
  - db.service.createArtist omitted canonical_name, same failure.

canonical_name holds the raw tag name, not normalize_artist() output,
which truncates on `/` and a standalone `x` ("AC/DC" -> "AC"). That is the
convention createLocalArtist already used. The truncation bug in
artists.name is pre-existing and deliberately left untouched here.

Verified on a scratch postgres:16-alpine with the real schema: the old
statement reproduces the NOT NULL violation, the new path yields
artists/albums/tracks/track_artists rows.

REVIEW-2026-07-30.md finding 1.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

workers/src/scanner.service.ts

@@ -237,9 +237,17 @@ export class ScannerService {
       return { id: String(found.rows[0].id), name: String(found.rows[0].name) };
     }
 
+    // `canonical_name` is NOT NULL in schema.sql with no default, so it MUST be
+    // supplied here — omitting it makes every artist insert fail on a fresh
+    // volume (and processFile swallows the error, so the scan silently yields an
+    // empty library). It holds the DISPLAY name: we store the raw tag name, not
+    // the normalize_artist() output, because that function truncates on `/` and
+    // a standalone `x` ("AC/DC" -> "AC", "Felix Mendelssohn" -> "Feli"). The
+    // enrichment path later overwrites canonical_name with the MusicBrainz name;
+    // until then the raw tag is the most faithful display value we have.
     const inserted = await this.pgClient.query(
-      'INSERT INTO artists (name) VALUES ($1) RETURNING id, name',
-      [name]
+      'INSERT INTO artists (name, canonical_name) VALUES ($1, $2) RETURNING id, name',
+      [name, rawName.trim() || name]
     );
     return { id: String(inserted.rows[0].id), name: String(inserted.rows[0].name) };
   }