[FEATURE]: Config option to disable syntax highlighting in diffs

[ibrahimsag]

Feature hasn't been suggested before.

• [x] I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Request

When viewing diffs in the TUI, syntax highlighting is always enabled. For some users/terminals, disabling syntax highlighting would improve readability.

Proposed solution:

Add a tui.diff_syntax boolean config option (default: true). When set to false, diffs render without syntax highlighting.

{
 tui: {
   diff_syntax: false
 }
}