[settings] Add back & properly implement use_dev_keys (#3631)

Was removed recently but also wasn't really working before, this adds it to the debug UI (under the kiosk option) and also makes it properly reload the keys on launch & setting change.

Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3631
Reviewed-by: crueter <crueter@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>
Co-authored-by: smiRaphi <neogt404@gmail.com>
Co-committed-by: smiRaphi <neogt404@gmail.com>

src/core/crypto/key_manager.h

@@ -1,4 +1,4 @@
-// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
 // SPDX-License-Identifier: GPL-3.0-or-later
 
 // SPDX-FileCopyrightText: Copyright 2018 yuzu Emulator Project
@@ -314,6 +314,7 @@ private:
     std::array<u8, 576> eticket_extended_kek{};
     RSAKeyPair<2048> eticket_rsa_keypair{};
 
+    bool dev_mode;
     void LoadFromFile(const std::filesystem::path& file_path, bool is_title_keys);
 
     template <size_t Size>