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/services/refresh_scheduler.h

@@ -34,6 +34,14 @@ public:
     static constexpr float kTxMaxAge = 15.0f;
     static constexpr float kOpidPoll = 2.0f;
 
+    // Low-impact polling profile applied while the daemon is SYNCING, regardless of the active tab.
+    // Only a slow progress poll runs (core, 10s); transactions/addresses/peers are disabled (0).
+    // Frequent getpeerinfo, per-block transaction scans, and balance polls all contend for the
+    // daemon's cs_main lock and measurably slow block connection during sync — this is exactly why
+    // the lightweight Console tab syncs faster than the Peers tab. Reverts to the per-tab profile
+    // once sync completes. (Tx/address/balance data is incomplete mid-sync anyway.)
+    static constexpr Intervals kSyncProfile{10.0f, 0.0f, 0.0f, 0.0f};
+
     static Intervals intervalsForPage(ui::NavPage page);
 
     void applyPage(ui::NavPage page);