Refactor Git panel styling & status colors for consistency (#26951)

Closes #26847

Release Notes:

- Updated Git panel background to use panel_background instead of
ElevationIndex::Surface.bg(cx) for consistency with other panels.
- Removed redundant GitStatusColors struct from status.rs and refactored
to use existing theme colors.
- Adjusted Color enum mappings in color.rs to reference
version_control_* colors instead of status() for better alignment with
the theme system.
- Cleaned up unused or redundant code.

crates/editor/src/items.rs

@@ -1673,13 +1673,13 @@ pub fn entry_diagnostic_aware_icon_decoration_and_color(
 pub fn entry_git_aware_label_color(git_status: GitSummary, ignored: bool, selected: bool) -> Color {
     let tracked = git_status.index + git_status.worktree;
     if ignored {
-        Color::Ignored
+        Color::VersionControlIgnored
     } else if git_status.conflict > 0 {
-        Color::Conflict
+        Color::VersionControlConflict
     } else if tracked.modified > 0 {
-        Color::Modified
+        Color::VersionControlModified
     } else if tracked.added > 0 || git_status.untracked > 0 {
-        Color::Created
+        Color::VersionControlAdded
     } else {
         entry_label_color(selected)
     }