feat(quote): add multi-level quote support with depth handling

- Implement nested quote blocks with depth levels (1-5)
- Combine sequential quotes with same depth into single block
- Add depth adjustment via keyboard shortcuts
- Improve quote styling with minimal visual indicators
- Update markdown parsing/serialization for depth support

Author: StringNick

components/editor/core/EditorCore.tsx

@@ -247,12 +247,15 @@ export const EditorCore = forwardRef<ExtendedMarkdownEditorRef, ExtendedMarkdown
 
       // Check for quote pattern (> text) - single line only
       if (!isMultiline) {
-        const quoteMatch = content.match(/^>\s+(.+)$/);
+        const quoteMatch = content.match(/^(>+)\s*(.*)$/);
         if (quoteMatch) {
+          const depth = quoteMatch[1].length;
+          const quoteContent = quoteMatch[2];
           return {
             ...updates,
             type: 'quote',
-            content: quoteMatch[1]
+            content: quoteContent,
+            meta: { depth }
           };
         }
       }