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/trigger_test.go

@@ -115,7 +115,8 @@ func TestTryStartScan_StaleInFlight_Reaps(t *testing.T) {
 		t.Errorf("existing = %v, want nil", existing)
 	}
 
-	// Verify the stale row was reaped: finished_at non-NULL, error_message contains "reaped".
+	// Verify the stale row was reaped: finished_at non-NULL, error_message
+	// contains "reaped".
 	var finishedAt pgtype.Timestamptz
 	var errMsg *string
 	if err := pool.QueryRow(context.Background(),