Add font size support to editor.

[Sachin1395]

Description

The editor currently supports basic text formatting (bold, italic, underline, headings),
but does not provide font size control.

Adding font size support would improve document formatting flexibility and usability.

Proposed Approach

• Use TipTap extension(s) to support custom font sizes
• Provide a UI control (dropdown or input) for selecting font size
• Apply font size to selected text only

Tasks

• Investigate TipTap support for font-size (e.g., TextStyle + custom commands)
• Implement font size extension
• Update toolbar UI with font size selector
• Ensure compatibility with collaborative editing (Yjs)
• Add basic documentation or usage notes

Acceptance Criteria

• Users can change font size for selected text
• Existing formatting remains unaffected
• Works correctly in collaborative sessions
• No regressions in editor behavior

Difficulty

Medium