perf(node): throttle RPC polling during sync so block download isn't slowed

The full-node wallet polled the daemon at the per-tab cadence regardless of sync state.
On the Peers/Network tab that meant getpeerinfo every 5s + core every 5s + a full
transaction scan on every new block — and blocks arrive fast during sync. Each of those
calls takes the daemon's cs_main lock, the same lock block connection needs, so the node
synced noticeably slower than on the lightweight Console tab (core 10s, no peer polling).

Make the refresh cadence sync-aware:
- RefreshScheduler::kSyncProfile {core 10s, transactions/addresses/peers disabled} is applied
  to ALL tabs while state_.sync.syncing, and reverts to the per-tab profile when sync ends.
  applyRefreshPolicy() picks the profile; update() re-applies it on the syncing<->synced
  transition. This suppresses getpeerinfo and the per-block tx scan during sync (that data is
  incomplete mid-sync anyway) — every tab now syncs as fast as Console.
- collectCoreRefreshResult(rpc, includeBalance): skip z_gettotalbalance (wallet lock + cs_main)
  while syncing; only getblockchaininfo runs, which is also what drives sync-progress detection.
  applyCoreRefreshResult already leaves the balance untouched when balanceOk is false.

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

src/app.h

@@ -519,6 +519,7 @@ private:
     int daemon_wait_attempts_ = 0;
     bool daemon_start_error_shown_ = false;
     int daemon_last_seen_crashes_ = 0;  // surface each new embedded-daemon crash reason once
+    bool refresh_policy_syncing_ = false;  // whether the sync-throttle refresh profile is active
     // Auto-clear for secrets copied to the clipboard. Only a hash of the copied secret is kept.
     std::uint64_t clipboard_secret_hash_ = 0;
     double clipboard_clear_deadline_ = 0.0;