fix(wallet): retire tracked sends that only paid the wallet itself

A send stays tracked until z_viewtransaction shows an outgoing output.
Shields, merges/consolidations and chat note splits pay only the wallet
itself, so they never showed one. They stayed tracked for the whole
session and forced a full history refresh past the scan throttle on
every tab.

- A tracked send whose view has no outgoing output is retired once it
  is mined (1+ confirmations) or conflicted.
- Tracked sends are enriched first, and reaching the per-cycle view cap
  no longer ends the loop, so the cap can't starve them.
- Backstop: a tracked send still unsettled 20 blocks after it was added
  (expired, dropped from the mempool) stops being tracked.
- Tracked sends are cleared on disconnect: they belong to that
  connection's wallet.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/app.cpp

@@ -1311,6 +1311,7 @@ void App::update()
                     successfulOpids.insert(opid);
                     markPendingSendTransactionSucceeded(opid, txid);
                     send_txids_.insert(txid);
+                    send_txid_heights_.emplace(txid, state_.sync.blocks);
                     invokeSendResultCallback(opid, true, txid);
                 }