fix: improve contrast for diff words, error, and git-deleted colors

P0 - Diff word colors (foreground on light diff backgrounds):
  diffAddedWord: rgb(36,138,61) → rgb(0,110,40)  (contrast 4.06→6.00:1)
  diffRemovedWord: rgb(207,34,46) → rgb(175,25,35) (contrast 4.21→5.50:1)

P1 - Error/gitDeleted red (human eye less sensitive to red wavelengths):
  error: #ef5350 → #ff5252 (Material Red A200, perceptually brighter)
  gitDeleted: #ef5350 → #ff5252 (matches error)

Co-Authored-By: DeepSeek <noreply@deepseek.com>

Author: jimgqyu

packages/cli/src/theme.ts

@@ -269,7 +269,7 @@ const DARK_FILETREE: FileTreeColors = {
   file: '#C0C0C0',
   gitAdded: '#4caf50',
   gitModified: '#ffa726',
-  gitDeleted: '#ef5350',
+  gitDeleted: '#ff5252',
   gitUntracked: '#9e9e9e',
 };
 
@@ -290,7 +290,7 @@ export const DARK_THEME: Theme = {
 
     label: '#F0C040',
     ok: '#4caf50',
-    error: '#ef5350',
+    error: '#ff5252',
     warn: '#ffa726',
 
     prompt: '#FFF8DC',
@@ -310,8 +310,8 @@ export const DARK_THEME: Theme = {
 
     diffAdded: 'rgb(220,255,220)',
     diffRemoved: 'rgb(255,220,220)',
-    diffAddedWord: 'rgb(36,138,61)',
-    diffRemovedWord: 'rgb(207,34,46)',
+    diffAddedWord: 'rgb(0,110,40)',
+    diffRemovedWord: 'rgb(175,25,35)',
     shellDollar: '#64B5F6'
   },