fix(sync): prioritize getblockchaininfo and pause chat scans while behind

The node kept falling behind the network near the tip because sync
DETECTION was starved: getblockchaininfo was queued behind the
O(mapWallet) wallet RPCs (z_gettotalbalance / z_listunspent), so
longestchain went stale, the wallet decided it was "synced", and it
resumed hammering cs_main — a feedback loop.

- Issue getblockchaininfo FIRST each cycle and skip the balance/address/
  tx refresh entirely while behind, so sync state (and kSyncProfile)
  updates before any heavy wallet scan runs.
- Gate the two chat note scans (refreshChatNoteBudgetNode /
  fastScanChatMemos) on effectivelySyncing() and the active page, so chat
  memo scanning no longer competes with block connection during sync.
- Windows debug.log tailer: reset the read offset when dragonxd truncates
  the log on startup (it was stranding at Block:0 with no witness/rescan
  progress).
- Tests cover the getblockchaininfo-first ordering and behind-skip.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/services/network_refresh_service.h

@@ -147,6 +147,14 @@ public:
         std::string errorMessage;
     };
 
+    // Minimal per-note view of a z_listunspent entry — just what a downstream consumer needs to derive
+    // spendable-note budgets without re-scanning. Kept UI/feature-agnostic (no chat specifics here).
+    struct UnspentNoteLite {
+        double amount = 0.0;      // note value, DRGX
+        bool   locked = false;    // tied up by an in-flight send
+        int    confirmations = 0; // TRUE depth (rawconfirmations when present, else confirmations)
+    };
+
     struct AddressRefreshResult {
         std::vector<AddressInfo> shieldedAddresses;
         std::vector<AddressInfo> transparentAddresses;
@@ -154,6 +162,12 @@ public:
         // lists may be falsely short. Consumers that treat an empty list as authoritative (e.g. the
         // empty-wallet warning) must not trust a 0 count unless this is true.
         bool addressListOk = true;
+        // Wall-clock spent in the address scan (dominated by z_listunspent — O(mapWallet), holds the
+        // daemon's cs_main). Lets the caller throttle how often it polls (addressRefreshDue()).
+        double scanMs = 0.0;
+        // The wallet's unspent notes from this same z_listunspent scan, so a consumer (e.g. the chat
+        // note-budget) can be fed for free instead of running its own duplicate z_listunspent.
+        std::vector<UnspentNoteLite> unspentNotes;
     };
 
     struct AddressRefreshSnapshot {
@@ -205,6 +219,9 @@ public:
         std::size_t shieldedAddressCount = 0;
         std::unordered_map<std::string, int> shieldedScanHeights;
         bool shieldedScanComplete = true;
+        // Wall-clock spent in the history scan (z_listreceivedbyaddress — O(mapWallet), holds cs_main).
+        // Lets the caller throttle the routine full rescan by its measured cost (txRefreshDue()).
+        double scanMs = 0.0;
     };
 
     struct OperationStatusPollResult {