Fix functional bugs found in UI audit

Send flow:
- "Sent" success now gates on the real dispatch result (NostrService send
  phase Working/Sent/Failed) instead of send_creating, which cleared before
  the DM left. Added a Failed stage with Try again / Close so a failed send
  is no longer shown as success.
- NIP-05 handle resolution moved off the UI thread (was .join()-blocking the
  render thread for the Tor timeout); now a worker thread writes into a polled
  slot with an inline "Looking up…" spinner.
- Desktop amount entry no longer steals keystrokes from the Note field (guards
  on the note TextEdit focus).
- Review screen now shows a network-fee line.

Requests / identity / archive:
- Approve is now double-tap safe (per-session approving set + disabled button),
  closing a double-pay window.
- "Backup nostr key" copied the public npub; split into "Copy npub (public)"
  and "Back up secret key (nsec)" which copies the real secret.
- Added inline username claim (availability check + NIP-98 register over Tor,
  off-thread) for anonymous users; persists nip05 + republishes identity.
- Added archive Export / Wipe history controls.
- Receive "Slatepack" button now copies the grin1 address; "Scan" tab relabeled
  "Receive" (no scanner was wired).
- Goblin view resets on wallet switch so a half-filled send can't leak across.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/wallet/wallet.rs

@@ -2123,6 +2123,7 @@ async fn handle_task(w: &Wallet, t: WalletTask) {
 				return;
 			};
 			w.send_creating.store(true, Ordering::Relaxed);
+			service.set_send_phase(crate::nostr::send_phase::WORKING);
 			match w.send(*a, None) {
 				Ok(s) => {
 					sync_wallet_data(&w, false);
@@ -2161,6 +2162,7 @@ async fn handle_task(w: &Wallet, t: WalletTask) {
 									contact.unknown = false;
 									service.store.save_contact(&contact);
 								}
+								service.set_send_phase(crate::nostr::send_phase::SENT);
 							}
 							Err(e) => {
 								error!("nostr send dispatch failed: {e}");
@@ -2176,14 +2178,19 @@ async fn handle_task(w: &Wallet, t: WalletTask) {
 										))),
 									);
 								}
+								service.set_send_phase(crate::nostr::send_phase::FAILED);
 							}
 						}
+					} else {
+						// No slatepack text produced — treat as failure.
+						service.set_send_phase(crate::nostr::send_phase::FAILED);
 					}
 					w.on_task_result(tx, &t);
 				}
 				Err(e) => {
 					error!("nostr send error: {:?}", e);
 					w.send_creating.store(false, Ordering::Relaxed);
+					service.set_send_phase(crate::nostr::send_phase::FAILED);
 				}
 			}
 		}