docs: the history phrases the id sweep missed, restated as present-tense facts or traps (#6277)

A wider pass for "previous", "before the fix", "we shipped" and the
like. The chi double-subtree, uppercase Vorbis key and stopPropagation
comments now describe the trap they guard; commit hashes, CI run
numbers and a deleted file name are gone; uuidString's comment says
what it returns.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/library/genre_test.go

@@ -334,7 +334,7 @@ func TestExtractGenres_EndToEnd(t *testing.T) {
 	if err != nil {
 		t.Fatalf("tag.ReadFrom: %v", err)
 	}
-	// Confirm the upstream behaviour this fix exists for is still present —
+	// Confirm the upstream behaviour this reader works around is still present —
 	// if dhowden ever fixes it, this test tells us the workaround can go.
 	if welded := meta.Genre(); welded != "Alternative RockRock" {
 		t.Logf("note: dhowden/tag no longer welds multi-values (got %q)", welded)