feat: RPC caching, background decrypt import, fast-lane peers, mining fix

RPC client:
- Add call() overload with per-call timeout parameter
- z_exportwallet uses 300s, z_importwallet uses 1200s timeout

Decrypt wallet (app_security.cpp, app.cpp):
- Show per-step and overall elapsed timers during decrypt flow
- Reduce dialog to 5 steps; close before key import begins
- Run z_importwallet on detached background thread
- Add pulsing "Importing keys..." status bar indicator
- Report success/failure via notifications instead of dialog

RPC caching (app_network.cpp, app.h):
- Cache z_viewtransaction results in viewtx_cache_ across refresh cycles
- Skip RPC calls for already-cached txids (biggest perf win)
- Build confirmed_tx_cache_ for deeply-confirmed transactions
- Clear all caches on disconnect
- Remove unused refreshTransactions() dead code

Peers (app_network.cpp, peers_tab.cpp):
- Route refreshPeerInfo() through fast_worker_ to avoid head-of-line blocking
- Replace footer "Refresh Peers" button with ICON_MD_REFRESH in toggle header
- Refresh button triggers both peer list and full blockchain data refresh

Mining (mining_tab.cpp):
- Allow pool mining toggle when blockchain is not synced
- Pool mining only needs xmrig, not local daemon sync

src/app.h

@@ -10,6 +10,8 @@
 #include <thread>
 #include <atomic>
 #include <chrono>
+#include <unordered_map>
+#include <unordered_set>
 #include "data/wallet_state.h"
 #include "rpc/connection.h"
 #include "ui/sidebar.h"
@@ -443,11 +445,40 @@ private:
 
     // P4: Incremental transaction cache
     int last_tx_block_height_ = -1;  // block height at last full tx fetch
+    float tx_age_timer_ = 0.0f;             // seconds since last tx fetch
+    static constexpr float TX_MAX_AGE = 15.0f; // force tx refresh every N seconds even without new blocks
+    static constexpr int MAX_VIEWTX_PER_CYCLE = 25; // cap z_viewtransaction calls per refresh
+
+    // P4b: z_viewtransaction result cache — avoids re-calling the RPC for
+    // txids we've already enriched.  Keyed by txid.
+    struct ViewTxCacheEntry {
+        std::string from_address;  // first spend address
+        struct Output {
+            std::string address;
+            double value = 0.0;
+            std::string memo;
+        };
+        std::vector<Output> outgoing_outputs;
+    };
+    std::unordered_map<std::string, ViewTxCacheEntry> viewtx_cache_;
+
+    // P4c: Confirmed transaction cache — deeply-confirmed txns (>= 10 confs)
+    // are accumulated here and reused across refresh cycles.  Only
+    // recent/unconfirmed txns are re-fetched from the daemon each time.
+    std::vector<TransactionInfo> confirmed_tx_cache_;
+    std::unordered_set<std::string> confirmed_tx_ids_;  // fast lookup
+    int confirmed_cache_block_ = -1;  // block height when cache was last built
 
     // Dirty flags for demand-driven refresh
     bool addresses_dirty_ = true;           // true → refreshAddresses() will run
+    bool transactions_dirty_ = false;       // true → force tx refresh regardless of block height
     bool encryption_state_prefetched_ = false; // suppress duplicate getwalletinfo on connect
 
+    // Pending z_sendmany operation tracking
+    std::vector<std::string> pending_opids_;  // opids to poll for completion
+    float opid_poll_timer_ = 0.0f;
+    static constexpr float OPID_POLL_INTERVAL = 2.0f;
+
     // First-run wizard state
     WizardPhase wizard_phase_ = WizardPhase::None;
     std::unique_ptr<util::Bootstrap> bootstrap_;
@@ -512,6 +543,9 @@ private:
     char decrypt_pass_buf_[256] = {};
     std::string decrypt_status_;
     bool decrypt_in_progress_ = false;
+    std::chrono::steady_clock::time_point decrypt_step_start_time_{};
+    std::chrono::steady_clock::time_point decrypt_overall_start_time_{};
+    std::atomic<bool> decrypt_import_active_{false};  // background z_importwallet running
 
     // Wizard PIN setup state
     char wizard_pin_buf_[16] = {};
@@ -544,7 +578,6 @@ private:
     void refreshData();
     void refreshBalance();
     void refreshAddresses();
-    void refreshTransactions();
     void refreshPrice();
     void refreshWalletEncryptionState();
     void checkAutoLock();