[Bug]: Keyboard shortcuts can't be set to mouse buttons

### Pre-flight checklist

- [x] I searched [existing issues](https://github.com/AprilNEA/OpenLogi/issues?q=is%3Aissue) and this is not a duplicate.
- [x] I am on the [latest release](https://github.com/AprilNEA/OpenLogi/releases/latest) or a recent `master` build.
- [x] I quit **Logi Options+** before running OpenLogi (the two apps fight over HID++ access and only one can own a receiver at a time).

### Which part of OpenLogi?

Not sure

### OpenLogi version

0.6.26

### Operating system

macOS

### OS version & architecture

macOS 26.5.2

### Device model

MX Master 4 + Bolt Receiver

### How is the device connected?

Logi Bolt receiver

### Affected area(s)

- [ ] Device discovery / detection
- [x] Button remapping
- [ ] DPI control
- [ ] SmartShift
- [ ] Per-application profiles
- [ ] Battery status
- [x] Settings / configuration (TOML)
- [ ] Auto-update
- [ ] Menu bar / tray
- [ ] Other

### What happened?

I can't bind any keyboard shortcuts to any mouse button. The option is just not there. Even for bluetooth option of this mouse.

### Steps to reproduce

1. Open mouse configuration
2. See no option when trying to change assign key

### Diagnostics report

```markdown
### OpenLogi Diagnostics

**App**
- OpenLogi (GUI): v0.6.26 (release)
- Agent: v0.6.26 (connected)
- IPC protocol: GUI 13 / agent 13
- Inventory: ready
- OS: macOS 26.5.2 (x86_64)
- Locale: en-US (UI: follow system)
- Accessibility: granted · Input hook: installed
- Launch at login: no · Menu bar: yes · Update check: on
- Running from: source build (dev)
- Config: schema 3 · 2 configured device(s) · thumbwheel 14

**Assets**
- Source: user cache · Index: loaded (210 models) · User cache: present
- Cache path: ~/.local/share/openlogi-dev/assets · Bundle assets: absent

**Devices (2)**
- MX Master 4 — mouse (codename: MX Master 4)
- Connection: Logi Bolt receiver · Online: yes · Battery: 50% (discharging, good)
- Capabilities: buttons=yes, pointer=yes, lighting=no
- DPI: 1000 dpi (range 200–8000, 157 steps)
- Model: 0b042 (wpid: b042, model-ids: b042/0000/0000, ext-model: 00)
- Transports: BTLE
- Render: mx_master_4 · Slot 2
- MX Master 4 — mouse (codename: MX Master 4)
- Connection: unknown · Online: no · Battery: n/a
- Capabilities: buttons=yes, pointer=yes, lighting=no
- Model: 0b042 (wpid: b042, model-ids: b042/0000/0000, ext-model: 00)
- Transports: BTLE
- Render: mx_master_4 · Slot 0

**Receivers (1)**
- Logi Bolt Receiver (VID 046d / PID c548)
```

### `openlogi list` output

```text

```

### Logs

```shell

```

### macOS permissions (if applicable)

- [x] OpenLogi has **Accessibility** permission (needed to remap buttons via the event tap).
- [x] OpenLogi has **Input Monitoring** permission (needed for Bluetooth-direct devices and capture).

Start with the mouse configuration and button-remapping UI, then trace how keyboard shortcuts are represented in the TOML settings. Reproduce the issue on macOS with the MX Master 4 and compare the available assignment options for Bluetooth and Bolt connections. Done means a keyboard shortcut can be selected and saved for a mouse button, with the behavior verified after restarting the app.

Written by the indexing model from the issue text.