refactor: improve codebase structure and Univer integration

- Add AGENTS.md knowledge base with project documentation
- Move UserPreferences model to separate models.py file
- Extract API_KEY to environment variable for security
- Enhance Univer Editor with PPTX support and improved UI
- Improve file system handling with binary file detection
- Add HF_ENDPOINT mirror for better China connectivity
- Clean up unused imports and code structure

vite.config.js

@@ -53,7 +53,17 @@ export default defineConfig({
     include: [
       '@milkdown/crepe',
       '@milkdown/vue',
-      '@milkdown/kit'
+      '@milkdown/kit',
+      '@univerjs/core',
+      '@univerjs/design',
+      '@univerjs/engine-render',
+      '@univerjs/engine-formula',
+      '@univerjs/ui',
+      '@univerjs/presets',
+      '@univerjs/preset-docs-core',
+      '@univerjs/preset-sheets-core',
+      '@univerjs/slides',
+      '@univerjs/slides-ui'
     ]
   }
 })