Outgoing echoes were recorded optimistically regardless of whether the broadcast
was actually submitted. Now broadcastChatMemos / broadcastChatMemosLite return
whether the send was submitted (false on immediate failures: not connected, no
spendable z-address, or a lite send already in progress), and the echo records a
ChatDelivery status (Sent / Failed). The Chat tab shows a "not sent" marker in
the error color on failed messages. The status persists in the DB (backward-
compatible: old rows deserialize as Sent).
(A later async failure — an opid that fails after submission — still surfaces via
the existing send-progress notification; only the submit gate is reflected here.)
Also removes the now-unused chat_readonly_note string (the composer replaced the
read-only footer). Test: delivery status round-trips through the DB. Verified:
Linux + Windows build with chat ON, ctest 100%, hygiene clean.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>