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/leveled.go

@@ -21,7 +21,7 @@ import (
 	"golang.org/x/sync/singleflight"
 )
 
-// Leveled streams (M464 #5001).
+// Leveled streams.
 //
 // Sonos and other UPnP renderers fetch a track's URL themselves, so the phone
 // that sent them there cannot change what they play. For them the server