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/tracknumber.go

@@ -9,7 +9,7 @@ import (
 
 // ReadTrackAndDisc reads a file's track and disc numbers. dhowden/tag reads a
 // Vorbis TRACKNUMBER or DISCNUMBER only as a bare number, but taggers also
-// write "3/20" there (Minstrel's own importer did until #6171), and that
+// write "3/20" there (as Minstrel's own importer once did), and that
 // reads as 0. For Vorbis the number before the slash is taken instead.
 func ReadTrackAndDisc(m tag.Metadata) (track, disc int) {
 	track, _ = m.Track()