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/ui/src/styles/color.rs

@@ -58,6 +58,16 @@ pub enum Color {
     Selected,
     /// A color used to indicate a successful operation or status.
     Success,
+    /// A version control color used to indicate a newly added file or content in version control.
+    VersionControlAdded,
+    /// A version control color used to indicate conflicting changes that need resolution.
+    VersionControlConflict,
+    /// A version control color used to indicate a file or content that has been deleted in version control.
+    VersionControlDeleted,
+    /// A version control color used to indicate files or content that is being ignored by version control.
+    VersionControlIgnored,
+    /// A version control color used to indicate modified files or content in version control.
+    VersionControlModified,
     /// A color used to indicate a warning condition.
     Warning,
 }
@@ -84,6 +94,11 @@ impl Color {
             Color::Error => cx.theme().status().error,
             Color::Selected => cx.theme().colors().text_accent,
             Color::Success => cx.theme().status().success,
+            Color::VersionControlAdded => cx.theme().colors().version_control_added,
+            Color::VersionControlConflict => cx.theme().colors().version_control_conflict,
+            Color::VersionControlDeleted => cx.theme().colors().version_control_deleted,
+            Color::VersionControlIgnored => cx.theme().colors().version_control_ignored,
+            Color::VersionControlModified => cx.theme().colors().version_control_modified,
             Color::Warning => cx.theme().status().warning,
             Color::Custom(color) => *color,
         }