Cohesive design language for notifications and cells across all products and platforms

### Your use case

hand in hand with other [Get Your Update issues](https://docs.google.com/spreadsheets/d/1SAcCgnHoze9Flqx-XXkC0B8iQyLnpylv2z4iidK0v-8/edit#gid=1808199479)

We need to define the ideal state for notifications visuals, colours, spacing, cell decoration, across all platforms. Then we will break the ideal state into chunks of work by platform that can be delivered. This includes EX.

All platforms should have an updated notifications language that in cohesive, consistent, and clear (including counts, badges, colours, layout, spacing)

Things to consider:
* Colours - grey, dark grey, red,
* Weights - bold, italics, neither
* Room types and tags: Low priority/mute, favourite, neither
* Spaces notifications
* Room list - spacing, timestamps, message previews, dots/counts
* Room header - notification panel, threads icon, voip icon,
* Mark as unread (simple) (link GH issue)

☝️ not a complete list...

### Have you considered any alternatives?

_No response_

### Additional context

_No response_

### Are you willing to provide a PR?

No