[Feature]: Readjust DPI Number Range / Rethink Slider

### 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

Most users don't use DPI settings next to 100 or 2600.
This large range makes it awkward to use the slider for usable ranges. There needs to be a better option.

### Proposed solution

**Slider + numeric field combo**

Pair the slider with an editable number box. The slider handles quick/coarse adjustment in the common range; the text field handles precise or extreme values. This is probably the single most common real-world solution because it sidesteps the scaling problem entirely. power users type, casual users drag.

### Alternatives considered

_No response_

### Related area(s)

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

### Additional context

_No response_

Start by locating the GUI DPI slider and the code that defines its current range. Review how DPI values are displayed and applied, then verify that the proposed slider-plus-number-field interaction supports common and extreme values without losing precision.

Written by the indexing model from the issue text.