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/song_link_test.go

@@ -168,8 +168,8 @@ func TestCrossReleaseLinkNeedsAutoResolve_Integration(t *testing.T) {
 
 // A merge keeps the removed copy's link to the song on another release,
 // whichever copy's id names the song. That copy has no song_id of its own,
-// and before the fix its link was lost whenever the random ids made it the
-// key (the flaky failure in run 8891).
+// and its link must survive whichever way the random ids fall, including when
+// they make it the key.
 func TestMergeInheritsSongLink_Integration(t *testing.T) {
 	for _, removeAlbumCut := range []bool{true, false} {
 		pool := newPool(t)