feat: thread footer component redesign (#3457)

This pull request refactors the `ThreadFooterComponent` to simplify its
styling and improve theme consistency. The main changes include removing
the SVG gradient background, consolidating styles using a new
`useStyles` hook, and updating the theme structure for thread footer
styling.

**Component and Styling Refactor:**

* Removed the SVG gradient and related code from
`ThreadFooterComponent`, replacing it with a solid background and border
styles for a cleaner, more maintainable look.
[[1]](diffhunk://#diff-1cfe74b5f4159c43463c57804451f86acc24a0adb2fc863b9824b4ce054615e1L99-R67)
[[2]](diffhunk://#diff-0a18f457fa158009da6dace44242bb3a526c6f1c1bbf61384be0ad0c3c53324cL1727-R1738)
* Consolidated styles into a new `useStyles` hook that uses theme
primitives and semantic colors, improving consistency and
maintainability.

**Theme Structure Updates:**

* Updated the theme type definition so that `thread.newThread` now
contains separate `container` and `text` style objects, supporting more
granular customization.
* Modified the default theme to provide empty `container` and `text`
objects for `thread.newThread`, aligning with the new structure.

**Minor Cleanups:**

* Removed unused imports and old style definitions from
`ThreadFooterComponent.tsx`.
[[1]](diffhunk://#diff-1cfe74b5f4159c43463c57804451f86acc24a0adb2fc863b9824b4ce054615e1L1-L3)
[[2]](diffhunk://#diff-1cfe74b5f4159c43463c57804451f86acc24a0adb2fc863b9824b4ce054615e1L18-R35)
* Updated the snapshot tests to reflect the new thread footer layout and
styling.
[[1]](diffhunk://#diff-0a18f457fa158009da6dace44242bb3a526c6f1c1bbf61384be0ad0c3c53324cL1401-L1413)
[[2]](diffhunk://#diff-0a18f457fa158009da6dace44242bb3a526c6f1c1bbf61384be0ad0c3c53324cL1727-R1738)

Author: khushal87