test: cover not-archived non-received unarchive branch

Remove an unrelated webhook email payload formatting plan doc that was
accidentally included in this feature branch, and add the missing
shouldCheckUnarchive case for a non-archived thread with a non-received
status so every branch of the predicate is exercised.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: bf78429e-573c-406c-9f7c-1d6e1bddbbb5

Author: AchoArnold

api/pkg/services/message_thread_service_test.go

@@ -19,4 +19,5 @@ func TestShouldCheckUnarchive(t *testing.T) {
 	assert.True(t, service.shouldCheckUnarchive(archived, received), "archived + inbound -> consult phone setting")
 	assert.False(t, service.shouldCheckUnarchive(archived, sent), "outbound status -> no check")
 	assert.False(t, service.shouldCheckUnarchive(notArchived, received), "already unarchived -> no check")
+	assert.False(t, service.shouldCheckUnarchive(notArchived, sent), "not archived + outbound -> no check")
 }