feat: add theme toggle component and theme store for light/dark mode support

- Implemented ThemeToggle component for switching between light, dark, and system themes.
- Created themeStore for managing theme state and persisting user preferences in localStorage.
- Added utility functions for error message sanitization to prevent sensitive data leakage.
- Developed proxy utility functions for API requests, including template variable replacement.
- Enhanced layout with dark mode styles and smooth transitions for theme changes.
- Updated main layout and page components to integrate theme toggle and improve accessibility.
- Added server-side proxy handling with validation and error sanitization for API requests.

.claude/settings.local.json

@@ -9,7 +9,13 @@
       "Bash(npm run build:*)",
       "Bash(npm run test:*)",
       "Bash(python -m py_compile:*)",
-      "Bash(node --check:*)"
+      "Bash(node --check:*)",
+      "Bash(ls:*)",
+      "Bash(findstr:*)",
+      "mcp__zai-mcp-server__analyze_image"
+    ],
+    "additionalDirectories": [
+      "c:\\Users\\meowr\\projects\\excel2json\\src\\lib"
     ]
   },
   "enableAllProjectMcpServers": true,