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/ui/explorer/explorer_block_cache.h

@@ -0,0 +1,70 @@
+#pragma once
+
+#include <cstdint>
+#include <map>
+#include <string>
+
+struct sqlite3;
+
+namespace dragonx {
+namespace ui {
+
+struct ExplorerBlockSummary {
+    int height = 0;
+    std::string hash;
+    int tx_count = 0;
+    int size = 0;
+    std::int64_t time = 0;
+    double difficulty = 0.0;
+};
+
+class ExplorerBlockCache {
+public:
+    struct SavedTipValidation {
+        bool needed = false;
+        int height = 0;
+        std::string expectedHash;
+    };
+
+    ExplorerBlockCache();
+    ExplorerBlockCache(std::string databasePath, std::string legacyJsonPath);
+    ~ExplorerBlockCache();
+
+    ExplorerBlockCache(const ExplorerBlockCache&) = delete;
+    ExplorerBlockCache& operator=(const ExplorerBlockCache&) = delete;
+
+    static std::string defaultDatabasePath();
+    static std::string defaultLegacyJsonPath();
+
+    bool ensureOpen();
+    bool isOpen() const { return db_ != nullptr; }
+    const std::string& databasePath() const { return database_path_; }
+
+    std::map<int, ExplorerBlockSummary> loadRange(int minHeight, int maxHeight);
+    bool storeBlock(const ExplorerBlockSummary& block);
+    int cachedBlockCount();
+    void clearBlocks();
+
+    SavedTipValidation prepareValidation(int currentHeight, const std::string& currentBestHash);
+    void applySavedTipValidation(const SavedTipValidation& validation,
+                                 const std::string& actualHash,
+                                 int currentHeight,
+                                 const std::string& currentBestHash);
+    void updateTip(int height, const std::string& hash);
+
+private:
+    bool exec(const char* sql);
+    std::string getMetaValue(const std::string& key);
+    int getMetaInt(const std::string& key, int fallback);
+    void setMetaValue(const std::string& key, const std::string& value);
+    bool createSchema();
+    void migrateLegacyJsonIfNeeded();
+    void close();
+
+    sqlite3* db_ = nullptr;
+    std::string database_path_;
+    std::string legacy_json_path_;
+};
+
+} // namespace ui
+} // namespace dragonx