CopyQ v14.0.0 losing track of encryption key

**Describe the bug**
CopyQ includes the useful feature to encrypt tab contents (thank you!). In Windows 11, the encryption key seems to get sporadically forgotten. Rebooting always fixes the issue.

**To Reproduce**
1. Enable tab encryption with external key store
3. Use CopyQ as normal
4. Eventually CopyQ may lose track of the encryption key

**Expected behavior**
No encryption issues.

**Version, OS and Environment**
CopyQ Clipboard Manager 14.0.0-gd935d521-v14.0.0
Qt: 6.10.2
KNotifications: 6.23.0
Compiler: MSVC
Arch: x86_64-little_endian-llp64
OS: Windows 11 Version 25H2
Audio: miniaudio 0.11.25

- Application Version v14.0.0
- Windows 11 25H2
- Scoop

**Additional context**

This log should be helpful:
```
[note: rebooted here]
[2026-03-26 05:33:17.996] Note : Starting server: CopyQ 14.0.0-gd935d521-v14.0.0
[2026-03-26 05:33:18.575] Note : [copyq.passwd] Loading password from system keychain
[2026-03-26 05:33:18.587] Note : [copyq.passwd] Encryption password loaded from system keychain
[2026-03-26 05:33:18.668] Warning : [default] QSystemTrayIcon::setVisible: No Icon set
[2026-03-26 05:43:33.940] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 05:45:20.083] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 05:45:54.163] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 05:46:04.591] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 05:49:41.110] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 06:02:58.852] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 06:07:53.153] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 06:14:46.410] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 06:15:46.081] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 06:18:09.288] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 06:18:16.920] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 06:20:37.311] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 06:29:28.789] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 06:30:02.892] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 06:30:42.033] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 06:45:03.544] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 07:40:05.962] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 07:40:51.571] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 07:47:14.108] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 07:47:14.108] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 07:47:36.590] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 07:47:45.655] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 07:51:22.496] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 07:52:57.414] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 07:58:36.455] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 07:58:36.456] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 07:58:36.587] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 08:44:57.925] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 08:47:43.839] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 09:23:35.303] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 09:24:57.941] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 09:25:32.862] Warning : [qt.qpa.mime] Retrying to obtain clipboard.
[2026-03-26 09:41:52.117] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[2026-03-26 10:02:45.054] ERROR : [copyq.serialize] Cannot decrypt data (v3): no valid encryption key provided
[note: rebooted here]
[2026-03-26 11:02:12.864] Note : Starting server: CopyQ 14.0.0-gd935d521-v14.0.0
[2026-03-26 11:02:13.381] Note : [copyq.passwd] Loading password from system keychain
[2026-03-26 11:02:13.381] Note : [copyq.passwd] Encryption password loaded from system keychain
[2026-03-26 11:02:13.436] Warning : [default] QSystemTrayIcon::setVisible: No Icon set
[note: CopyQ working again]
```