feat(wallet): persist history and surface pending sends

Add an encrypted SQLite transaction history cache with cached tip metadata and
per-address shielded scan progress so startup and full refreshes avoid
re-scanning every z-address while still invalidating on wallet/address/rescan
changes.

Improve wallet history loading by paging transparent transactions, preserving
cached shielded and sent rows, keeping recent/unconfirmed activity visible, and
classifying mining-address receives. Show z_sendmany opid sends immediately in
History and Overview, pin pending rows through refreshes, and apply optimistic
address/balance debits until opids resolve.

Add timestamped RPC console tracing by source/method without logging params or
results, reduce redundant refresh/RPC calls, and cache Explorer recent block
summaries in SQLite.

Expand focused tests for transaction cache encryption, scan-progress
persistence/invalidation, history preservation, operation-status parsing,
pending send visibility, and Explorer/RPC refresh behavior.

src/rpc/rpc_client.h

@@ -25,6 +25,20 @@ using ErrorCallback = std::function<void(const std::string&)>;
  */
 class RPCClient {
 public:
+    using TraceCallback = std::function<void(const std::string& source, const std::string& method)>;
+
+    class TraceScope {
+    public:
+        explicit TraceScope(std::string source);
+        ~TraceScope();
+
+        TraceScope(const TraceScope&) = delete;
+        TraceScope& operator=(const TraceScope&) = delete;
+
+    private:
+        std::string previous_;
+    };
+
     RPCClient();
     ~RPCClient();
 
@@ -74,6 +88,13 @@ public:
      * @brief Get the error message from the last failed connect() attempt.
      */
     const std::string& getLastConnectError() const { return last_connect_error_; }
+    json getLastConnectInfo() const;
+
+    static void setTraceCallback(TraceCallback callback);
+    static void setTraceEnabled(bool enabled);
+    static bool isTraceEnabled();
+    static std::string currentTraceSource();
+    static void setTraceSource(std::string source);
 
     /**
      * @brief Make a raw RPC call
@@ -202,6 +223,7 @@ private:
     bool warming_up_ = false;
     std::string warmup_status_;
     std::string last_connect_error_;
+    json last_connect_info_;
     mutable std::recursive_mutex curl_mutex_;  // serializes all curl handle access
 
     // HTTP client (implementation hidden)