perf(history): add a transactions revision counter to WalletState

WalletState had no change signal for its transaction list, so a UI
cache had to fingerprint all N transactions every frame to notice an
update. It now carries tx_revision, a counter that only increases;
clear() on disconnect bumps it instead of resetting it, so a cache
built before a reconnect or wallet switch can never match again.

- Every writer of the list bumps it: the full-node refresh, loading the
  cached history, adding, completing and removing a pending send, a
  mining-address relabel, the lite refresh and the screenshot demo
  rows.
- The full-node refresh and the lite refresh (every ~2 s) swap in the
  new list only when it differs field by field, the amount compared
  bit-exactly because -0.0 and +0.0 print differently. An unchanged
  refresh keeps the list and the revision; the compare costs O(N) per
  refresh, not per frame.

Nothing reads the counter yet.

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

src/app_sweep.cpp

@@ -201,6 +201,7 @@ void App::installDemoWalletData()
         tx("deadbeef000000000000000000000000000000000000000000000000000000000000", "receive", 0.50000000,
            1751290000, 0, "zs1demosecondaryshieldedaddressforuisweep0000000000000000000000000", "pending"),
     };
+    state_.touchTransactions();
 
     // Demo portfolio groups so the Market tab's row styles render with real-looking data. Snapshot
     // the user's real portfolio first; setPortfolio* only mutate memory (save() is never called
@@ -261,6 +262,7 @@ void App::clearDemoWalletData()
     state_.totalBalance = s.totalBalance; state_.unconfirmedBalance = s.unconfirmedBalance;
     state_.addresses = s.addresses; state_.z_addresses = s.z_addresses; state_.t_addresses = s.t_addresses;
     state_.transactions = s.transactions;
+    state_.touchTransactions();
     state_.market.price_usd = s.market_price_usd;
     state_.market.change_24h = s.market_change_24h;
     state_.market.price_history = g_marketHistorySnapshot;