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/loudness_backfill_test.go

@@ -132,7 +132,7 @@ func TestLoudnessBackfill_Integration(t *testing.T) {
 	}
 
 	// Each stored measurement told the sync feed, so caching clients re-read
-	// the track and pick up its gain (#4997).
+	// the track and pick up its gain.
 	var logged int
 	if err := pool.QueryRow(ctx, `SELECT count(*) FROM library_changes
 	                               WHERE entity_type = 'track' AND op = 'upsert' AND entity_id = $1`,