docs: library comments say what the scanner and resolver do, not how they came to be (#6277)

Rewrites the internal/library comment blocks to rule 32. Task, milestone,
decision and rule ids are gone; the incidents behind them are restated as
the constraint they left (why a file is deleted before its row, why the
missing mark is a mark, why duplicates block on duration). Counts and
album names from one library are dropped from production comments; test
comments keep the names their fixtures use. The tagReadVersion log keeps
each version's before and after, without the measurements.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/library/mbidbackfill.go

@@ -18,9 +18,9 @@ import (
 const pgUniqueViolation = "23505"
 
 // isUniqueViolation reports whether err is a Postgres unique-constraint
-// conflict. Used to distinguish "another row already owns this MBID"
-// (a duplicate album/artist row in our DB, the operator should merge
-// it) from genuine write failures.
+// conflict. Used to distinguish "another row already owns this MBID" (a
+// duplicate album/artist row in our DB, for an admin to merge) from genuine
+// write failures.
 func isUniqueViolation(err error) bool {
 	var pgErr *pgconn.PgError
 	return errors.As(err, &pgErr) && pgErr.Code == pgUniqueViolation
@@ -31,7 +31,7 @@ type BackfillMBIDsResult struct {
 	Processed  int // Albums considered (mbid IS NULL).
 	Healed     int // Albums whose mbid we set.
 	Skipped    int // Albums where the file was missing or had no MBID tag.
-	Duplicates int // Albums whose mbid is already held by another row (operator-resolvable).
+	Duplicates int // Albums whose mbid another row already holds; an admin merges.
 }
 
 // BackfillMBIDs walks albums with NULL mbid, opens one track per album,