Add open/close transition animations to SearchBar, image popover, delete confirm modal, and page routing

- SearchBar: overlay fade + panel slide-down with spring enter / ease-in exit (200ms)
- MarkdownToolbar image popover: scale+slide with same pattern (180ms)
- ConfirmModal: new component replacing window.confirm, scale+translate animations
- AdminPage: uses ConfirmModal for article deletion
- AppShell: enter-only page transition (key={location.key}) avoids double-load issue

All @keyframes defined locally in each CSS module to ensure reliable scoping.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/settings.local.json

@@ -6,7 +6,11 @@
       "mcp__Claude_in_Chrome__tabs_context_mcp",
       "Bash(git init *)",
       "Bash(git add *)",
-      "Bash(git commit -m ' *)"
+      "Bash(git commit -m ' *)",
+      "Bash(git remote *)",
+      "Bash(git push *)",
+      "Bash(git commit -m 'docs: 重写 README 为中文，添加英文版跳转链接 *)",
+      "Bash(git commit -m 'Add open/close transition animations to SearchBar, image popover, delete confirm modal, and page routing *)"
     ]
   }
 }