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/daemon/embedded_daemon.h

@@ -183,6 +183,12 @@ public:
     void setRescanOnNextStart(bool v) { rescan_on_next_start_ = v; }
     bool rescanOnNextStart() const { return rescan_on_next_start_.load(); }
 
+    // Active wallet file (multi-wallet). Passed to the daemon as -wallet=<name> so it loads
+    // <datadir>/<name>; empty or "wallet.dat" keeps the daemon default (no arg). Must be a plain
+    // filename in the datadir — the daemon rejects paths.
+    void setWalletFile(const std::string& v) { wallet_file_ = v; }
+    std::string walletFile() const { return wallet_file_; }
+
     /**
      * @brief Request a wallet repair (-zapwallettxes=2) on the next daemon start. This deletes all
      *        wallet transaction/note records and rebuilds them from the chain (keys are kept); the
@@ -251,6 +257,7 @@ private:
     std::atomic<bool> should_stop_{false};
     std::set<std::string> debug_categories_;
     int max_connections_ = 0;  // 0 = daemon default
+    std::string wallet_file_;  // -wallet=<name> for the active wallet; empty/"wallet.dat" = default
     std::atomic<int> crash_count_{0};  // consecutive crash counter
     std::atomic<bool> rescan_on_next_start_{false};  // -rescan flag for next start
     std::atomic<bool> zap_on_next_start_{false};     // -zapwallettxes=2 flag for next start