feat(editor): add file upload and fix critical bugs

- Add markdown file upload functionality with upload button
- Fix error handling to throw errors instead of silently returning empty strings
- Fix memory leak by cleaning up debounceTimer in onUnmounted
- Update debounce timing from 150ms to 500ms for stability
- Enhance UI with floating action buttons and extensive style refinements
- Hide toolbar, menu, and line number elements for cleaner interface

plans/inline-suggestions-plan.md

@@ -39,7 +39,7 @@ import { Plugin, PluginKey } from '@milkdown/prose/state';
 import { EditorView } from '@milkdown/prose/view';
 
 const INLINE_SUGGESTION_KEY = new PluginKey('inline-suggestion');
-const DEBOUNCE_MS = 150;
+const DEBOUNCE_MS = 500;
 
 interface InlineSuggestionOptions {
     apiUrl?: string;