feat(lite): wallet encryption controller layer (encrypt/unlock/lock/decrypt)

Wire the backend passphrase-encryption commands into LiteWalletController:

- encryptWallet / decryptWallet (take passphrase by value, securely wipe it,
  save after), unlockWallet / lockWallet (bring spending keys into/out of
  memory), and encryptionStatus() -> {encrypted, locked}. All return
  failure-safe results; errors arrive as {"error":..} or "Error:" (handled).
- Fold encryptionstatus into refreshModel() (polled every cycle, available even
  mid-sync since it reads local wallet state) and apply it in
  applyLiteRefreshModelToWalletState, so WalletState.isEncrypted()/isLocked()
  track the backend — which gates the existing locked/auto-lock UI.

Backend contracts verified against the SDXL source: encrypt/unlock/decrypt take
the passphrase as the single arg; lock takes none; encryptionstatus returns
{"encrypted","locked"}; ops return {"result":"success"} / {"error":..}.

Tests: testLiteWalletControllerEncryption drives encrypt -> lock -> unlock ->
decrypt via encryptionStatus(), checks empty-passphrase + closed-wallet rejection,
and that the status folds into WalletState. Fake models the state machine.

GUI wiring (encrypt in Settings, unlock prompt / lock action) is the follow-up;
the backend create flow remains unencrypted by default until encrypt is run.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/wallet/lite_wallet_controller.h

@@ -106,6 +106,21 @@ struct LiteSeedResult {
     std::string error;
 };
 
+// Wallet encryption state (from the backend `encryptionstatus`). `locked` means the spending
+// keys are not in memory (an encrypted wallet loads locked; unlock to spend).
+struct LiteEncryptionStatus {
+    bool ok = false;
+    bool encrypted = false;
+    bool locked = false;
+    std::string error;
+};
+
+// Result of an encrypt/decrypt operation (the passphrase is wiped by the controller).
+struct LiteEncryptionResult {
+    bool ok = false;
+    std::string error;
+};
+
 class LiteWalletController {
 public:
     LiteWalletController(WalletCapabilities capabilities,
@@ -182,6 +197,16 @@ public:
     // Returns false when no wallet is open or the backend save fails.
     bool saveWallet();
 
+    // --- Wallet encryption (passphrase). All take the passphrase BY VALUE and securely wipe it. ---
+    // encrypt: set a passphrase on an unencrypted wallet. unlock/lock: bring the spending keys
+    // into / out of memory. decrypt: permanently remove encryption. encryptionStatus: query state
+    // (also folded into the periodic refresh so WalletState.isLocked()/isEncrypted() track it).
+    LiteEncryptionResult encryptWallet(std::string passphrase);
+    bool unlockWallet(std::string passphrase);
+    bool lockWallet();
+    LiteEncryptionResult decryptWallet(std::string passphrase);
+    LiteEncryptionStatus encryptionStatus();
+
     // Poll sync status + fetch balance/addresses/transactions, and apply the result into the
     // app's WalletState. Returns true if state was updated. Safe no-op when no wallet is open.
     // Synchronous (blocks on the backend); used by tests and as the worker's unit of work.