[Feature/bug]: Merge bluetooth and logitech dongle into one device.

### Pre-flight checklist

- [x] I searched existing issues and the [Roadmap](https://github.com/AprilNEA/OpenLogi#roadmap), and this isn't already tracked.

### Problem / motivation

In my view, the device should be one. To me the different connections behaves as different devices – and I would like my settings to follow device – not connection.

### Proposed solution

I would merge the items into one, and then the active icon can for instance be in color and the one not being used be grayscale. Settings follows device, not connection type (ie. I want my reverse scroll to work with both bluetooth and Logitech dongle)

### Alternatives considered

_No response_

### Related area(s)

- [x] GUI
- [ ] CLI
- [ ] Button actions / remapping
- [ ] DPI
- [ ] SmartShift
- [ ] Per-application profiles
- [ ] Configuration (TOML)
- [ ] Auto-update
- [ ] Other

### Additional context

### OpenLogi Diagnostics

**App**
- OpenLogi (GUI): v0.8.1 (release)
- Agent: v0.8.1 (connected)
- IPC protocol: GUI 28 / agent 28
- Inventory: ready
- OS: macOS 26.6.2 (arm64)
- Locale: en-GB (UI: follow system)
- Accessibility: granted · Input hook: installed
- Launch at login: yes · Menu bar: yes · Update check: on
- Running from: source build (dev)
- Config: schema 6 · 4 configured device(s) · thumbwheel 14

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

**Devices (4)**
- MX Master 3 — mouse (codename: Wireless Mouse MX Master 3)
- Connection: Logi Unifying receiver · Online: yes · Battery: 100% (discharging, full)
- Capabilities: buttons=yes, pointer=yes, lighting=no
- DPI: 1000 dpi (range 200–4000, 77 steps)
- Model: 0b023 (wpid: 4082, model-ids: b023/4082/0000, ext-model: 00)
- Transports: eQuad, BTLE
- Render: mx_master_3 · Slot 1
- MX Keys for Mac — keyboard (codename: MX Keys for Mac)
- Connection: Logi Unifying receiver · Online: yes · Battery: 0% (full, critical)
- Capabilities: buttons=yes, pointer=no, lighting=no
- Model: 2b361 (wpid: 4092, model-ids: b361/4092/0000, ext-model: 02)
- Transports: eQuad, BTLE
- Render: mx_keys_mac · Slot 2
- MX Master 3 — mouse (codename: Wireless Mouse MX Master 3)
- Connection: unknown · Online: no · Battery: n/a
- Capabilities: buttons=yes, pointer=yes, lighting=no
- Model: 0b023 (wpid: 4082, model-ids: b023/4082/0000, ext-model: 00)
- Transports: eQuad, BTLE
- Render: mx_master_3 · Slot 0
- MX Keys for Mac — keyboard (codename: MX Keys for Mac)
- Connection: unknown · Online: no · Battery: n/a
- Capabilities: buttons=yes, pointer=no, lighting=no
- Model: 2b361 (wpid: 4092, model-ids: b361/4092/0000, ext-model: 02)
- Transports: eQuad, BTLE
- Render: mx_keys_mac · Slot 0

**Receivers (1)**
- Unifying Receiver (VID 046d / PID c52b)

Start by tracing the GUI device inventory and how model IDs, transports, connection state, and settings are represented. Determine how Bluetooth and Logitech dongle entries for the same device can share settings while showing active and inactive connection states; done when each physical device appears once and its settings apply across both connections.

Written by the indexing model from the issue text.