feat(lite): auto-open existing wallet on startup + gate full-node RPC refreshes

Auto-open: on the first update() tick (kept off init() so a slow
initialize_existing network call can't freeze startup before the window), if a
wallet file exists, open it. initialize_existing needs no passphrase — it loads
the file; a previously-synced + saved wallet resumes from its height (fast)
instead of rescanning from the checkpoint. Adds LiteWalletController::walletExists()
(bridge.walletExists on the connection's chain) + a chainName_ member.

RPC-refresh gating: the earlier connected=walletOpen() fix (so the wallet UI is
enabled in lite) had a side effect — the full-node periodic + per-page RPC
refreshes (mining/balance/peers/txs, and setCurrentPage's immediate refresh)
gate on state_.connected, so they began firing in lite and failing
("X error: Not connected"). Re-gate those on ACTUAL RPC connectivity
(rpc_ && rpc_->isConnected()) instead of the lite proxy. Full-node is unchanged
(state_.connected ⟺ rpc connected there); lite no longer issues any RPC.

Runtime-verified in WSLg with a pre-seeded wallet: app auto-opens (Starting
Mempool + sync begins), and "Not connected" / getMiningInfo / RPC-connect noise
all drop to 0 — a fully clean lite run. tests pass.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app_network.cpp

@@ -565,8 +565,10 @@ void App::setCurrentPage(ui::NavPage page)
     applyRefreshPolicy(page);
     using RefreshTimer = services::NetworkRefreshService::Timer;
 
-    // Immediate refresh for the incoming tab's priority data
-    if (state_.connected && !state_.isLocked()) {
+    // Immediate refresh for the incoming tab's priority data. Gate on ACTUAL RPC connectivity
+    // (not state_.connected, which is the lite "online" proxy) — lite has no RPC daemon and the
+    // lite controller refreshes wallet data itself, so these full-node RPC polls must not fire.
+    if (rpc_ && rpc_->isConnected() && !state_.isLocked()) {
         using NP = ui::NavPage;
         switch (page) {
             case NP::Overview: