Task #520: skip send-note confirm when only one recipient

The send-note composer always showed an AlertDialog before posting,
even for the common one-on-one case. The dialog now only appears when
two or more recipients are picked.

Implementation (artifacts/tx-os/src/pages/notes.tsx):
- Extracted shared `performSend()` from `confirmSubmit` so both the
  direct-send and confirm-then-send paths reuse the same mutation,
  success toast + composer close, and error toast.
- `requestSubmit()` now branches: 0 picked = no-op, 1 picked = call
  performSend() directly, 2+ picked = open the existing AlertDialog.
- `confirmSubmit()` (the AlertDialog action) delegates to performSend.
- No changes to API, recipient picker, AR/EN strings, or any other
  AlertDialog (bulk archive/delete left untouched).

Tests:
- Updated artifacts/tx-os/tests/notes-inbox.spec.mjs (sends to a
  single recipient): no longer expects the confirm dialog; asserts
  /api/notes/:id/send fires directly and the composer closes.
- New artifacts/tx-os/tests/notes-send-confirm-threshold.spec.mjs:
  - "single-recipient send skips the confirm dialog" (passes)
  - "multi-recipient send still requires the confirm dialog" (passes)

Validation: tx-os tsc clean; both threshold specs pass locally;
architect review APPROVED.

artifacts/tx-os/src/pages/notes.tsx

@@ -2513,10 +2513,6 @@ function SendNoteDialog({
 
   const [confirmOpen, setConfirmOpen] = useState(false);
 
-  // Task #520: skip the confirmation dialog when sending to a single
-  // recipient. The dialog only added an extra click for the common
-  // one-on-one case; it still appears when 2+ recipients are picked so
-  // a batch send remains an explicit choice.
   const performSend = () => {
     send.mutate(
       { id: noteId, recipientUserIds: Array.from(picked) },