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/mbidbackfill_test.go

@@ -13,8 +13,8 @@ import (
 )
 
 // The MBID backfills read tags from files, so a track whose file is gone has
-// nothing to give them. Before #5139 they opened it anyway, and every scan
-// logged an "open failed" warning per missing track.
+// nothing to give them: they skip it rather than log an "open failed" warning
+// per missing track on every scan.
 func TestMBIDBackfill_SkipsMissingTracks_Integration(t *testing.T) {
 	pool := newPool(t)
 	ctx := context.Background()