Umbriel support

### Feature Description

Would there be a possibility of supporting matugen colors for Umbriel, and maybe integration? Keybinds, gaps, radius, etc

### Use Case

Here's a mockup template I'm currently using, it's based off the one for Niri (probably needs some changes):

```
[colors]
background = "{{colors.surface_container.default.hex}}F0"
text_primary = "{{colors.on_surface.default.hex}}FF"
text_muted = "{{colors.on_surface_variant.default.hex}}FF"
accent_primary = "{{colors.primary.default.hex}}FF"
accent_secondary = "{{colors.secondary.default.hex}}FF"
warning = "{{colors.tertiary.default.hex}}FF"
error = "{{colors.error.default.hex}}FF"

[appearance]
border_focused = "{{colors.primary.default.hex}}FF"
border_unfocused = "{{colors.outline.default.hex}}FF"
scratchpad_border_focused = "{{colors.primary.default.hex}}FF"
scratchpad_border_unfocused = "{{colors.outline.default.hex}}FF"
outer_border_color = "{{colors.surface_container_lowest.default.hex}}FF"
insert_hint_color = "{{colors.primary.default.hex}}80"
backdrop_color = "{{colors.surface_variant.default.hex}}FF"

[overview]
background_tint = "{{colors.surface.default.hex}}30"
```

### Compositor(s)

Other (specify below)

### If Other, please specify

Umbriel

### Proposed Solution

_No response_

### Alternatives/Existing Solutions

_No response_

No file, test, or entry point is named. Start by reviewing the existing compositor integrations and the Niri-based matugen template mentioned in the issue, then clarify whether the goal is color support, keybinds, gaps, radius, or broader integration. Done should mean an agreed Umbriel support scope is implemented and verified.

Written by the indexing model from the issue text.