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/ui/pages/settings_page.cpp

@@ -40,6 +40,7 @@
 #include "../windows/export_transactions_dialog.h"
 #include "../windows/bootstrap_download_dialog.h"
 #include "../windows/daemon_download_dialog.h"
+#include "../windows/wallets_dialog.h"
 #include "../../embedded/IconsMaterialDesign.h"
 #include "imgui.h"
 #include <nlohmann/json.hpp>
@@ -1340,6 +1341,11 @@ void RenderSettingsPage(App* app) {
                 if (TactileButton(TR("seed_migrate_button"), ImVec2(0, 0), btnFont))
                     app->showSeedMigrationDialog();
                 if (ImGui::IsItemHovered()) material::Tooltip("%s", TR("tt_seed_migrate"));
+                // Multi-wallet: list wallet files + switch the active one.
+                ImGui::SameLine(0, scaledSp);
+                if (TactileButton(TR("wallets_button"), ImVec2(0, 0), btnFont))
+                    ui::WalletsDialog::show(app);
+                if (ImGui::IsItemHovered()) material::Tooltip("%s", TR("tt_wallets_button"));
             }
             ImGui::SameLine(0, scaledSp);
             if (TactileButton(r1[4], ImVec2(0, 0), btnFont))