feat(developer): Font Audit Review Window

### Is your feature request related to a problem? Please describe.

When working on a new keyboard, it would be helpful to have a way to check if any key sequences were missed for a target orthography or set of targetted symbols. This would be particularly useful when working on a script that is unfamiliar to the keyboard developer. Also when working on a keyboard for experimental orthographies where it is easy to overlook unfamiliar symbols that may look very similar.

### Describe the solution you'd like

A window or panel that would present a font menu. The user would select a font from the menu and a scrollable grid of letters and symbols would be presented. The background color of the glyphs with codepoints that are unreachable by the keyboard (not emitted) would be made a light red. Clicking on a glyph a status area could show the composition sequence and line number where it can be found.

### Describe alternatives you've considered

_No response_

### Related issues

_No response_

### Keyman apps

- [ ] Keyman for Android
- [ ] Keyman for iPhone and iPad
- [ ] Keyman for Linux
- [ ] Keyman for macOS
- [ ] Keyman for Windows
- [x] Keyman Developer
- [ ] KeymanWeb
- [ ] Other - give details at bottom of form

### Keyman version

Current version

### Operating system

Windows

### Device

laptop

### Target application

N/A

### Browser

N/A

### Keyboard name

N/A

### Keyboard version

N/A

### Language name

N/A

### Additional context

_No response_

The issue names no files, tests, or existing entry points. Start by locating the Keyman Developer UI entry point and the data used for keyboard output; define the font selection, scrollable glyph grid, unreachable-codepoint highlighting, and click-to-status behavior before implementation.

Written by the indexing model from the issue text.