Keep the notifications worth interrupting for

Splitting system messages out of the modal was right for payout receipts,
but it would have silenced two that a member genuinely loses money by
ignoring:

  - "@someone is trying to buy. Link your wallet so it pays you" — a sale
    is blocked right now, and the referral is lost permanently once it
    routes to someone else.
  - "You missed 43 POL on InstantAdPay" — a payout passed them by, and the
    message explains exactly how to stop the next one doing the same.

So the dividing line is not system-versus-human, it is "does this need you
to do something". Those two become kind 'alert' and still interrupt; the
receipts stay kind 'notice' and stay in the inbox.

The modal no longer credits an alert to a person either. It was saying "A
message from @martbost" over machine-generated text, because system mail
is sent by member 1 at ADMIN_EMAIL. Alerts now read "Action needed on your
account".

Also reclassified "X is now in your line for good" as a notice — it is
good news about a referral the member gained, with nothing at stake.

qa/messages-notice.mjs now covers both lanes: 14 checks, including that an
alert interrupts and a flood of 25 receipts does not.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

public/my.html

@@ -1033,7 +1033,7 @@
 <script src="/assets/common.js?v=20260916a"></script>
 <script src="/assets/wallet.js?v=20260911a"></script>
 <script src="/assets/promo.js?v=20260911a"></script>
-<script src="/assets/my.js?v=20260918a"></script>
+<script src="/assets/my.js?v=20260918b"></script>
 <script src="/assets/chat.js?v=20260907l"></script>
 </body>
 </html>