feat(wallet): wallet-files list + switching (P2)

Second phase of multi-wallet: list wallet files and switch the active one.

- Daemon plumbing: EmbeddedDaemon::setWalletFile -> start() passes -wallet=<name>
  (non-default only; skipped during the isolated seed-migration start), and
  DaemonController::syncSettings pushes active_wallet_file on each start.
- App::switchToWallet: persist the new active wallet, then stop + restart the
  node on -wallet=<name> (rescan only if it was never synced in this datadir).
  Reuses the seed-adopt restart coordination; WalletState clears on disconnect
  and the P1 identity-scoped caches re-key, so no previous-wallet data leaks.
  Guarded: full-node, embedded daemon, not mid-restart, no pending send.
- Wallets dialog (Settings -> Backup & Data -> "Wallets…"): a table of wallet
  files (datadir wallet*.dat + user-added folders' *.dat) with size (disk) and
  cached balance / address count / last-opened (wallet index), a current/Active
  badge, Open (switch), and Add folder. Out-of-datadir wallets show "import to
  open" (P3). Added as a sweep surface.
- Mining payout safety: non-destructive warning if the pool-mode worker looks
  like a DragonX address not in the current wallet (stale after a switch).

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

src/app.h

@@ -202,6 +202,9 @@ public:
     // per-wallet data (e.g. address-book contacts). Empty until addresses are known (pre-connect).
     std::string activeWalletIdentityHash() const;
 
+    data::WalletIndex& walletIndex() { return wallet_index_; }
+    const data::WalletIndex& walletIndex() const { return wallet_index_; }
+
     // Connection state (convenience wrappers)
     bool isConnected() const { return state_.connected; }
     int getBlockHeight() const { return state_.sync.blocks; }
@@ -447,6 +450,10 @@ public:
      * Shows "Restarting daemon..." in the loading overlay while the daemon cycles.
      */
     void restartDaemon();
+    // Switch the active wallet: persist the new -wallet=<name>, stop the node, restart on it
+    // (rescan only if it was never synced in this datadir). Per-wallet data follows automatically
+    // via the identity-scoped caches (P1). No-op if that wallet is already active.
+    void switchToWallet(const std::string& walletFile);
 
     // Wallet encryption helpers
     void encryptWalletWithPassphrase(const std::string& passphrase);