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/source_markers_test.go

@@ -5,7 +5,7 @@ import (
 	"testing"
 )
 
-// Real basenames from the operator's library (2026-10-08), each with the
+// Real basenames, each with the
 // labels it should carry. The negatives are the near misses that shaped the
 // list: a song called "Chain Reaction", a live album, an ordinary track.
 func TestSourceMarkersFor(t *testing.T) {