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.cpp

@@ -54,6 +54,7 @@
 #include "ui/windows/bootstrap_download_dialog.h"
 #include "ui/windows/xmrig_download_dialog.h"
 #include "ui/windows/daemon_download_dialog.h"
+#include "ui/windows/wallets_dialog.h"
 #include "ui/windows/console_tab.h"
 #include "ui/pages/settings_page.h"
 #include "ui/theme.h"
@@ -1990,6 +1991,7 @@ void App::render()
     ui::BootstrapDownloadDialog::render();
     ui::XmrigDownloadDialog::render();
     ui::DaemonUpdateDialog::render();
+    ui::WalletsDialog::render();
 
     // Windows Defender antivirus help dialog
     renderAntivirusHelpDialog();