[website] Improve typography by adopting Inter font

[wuchong]

Purpose

This PR updates the primary font family of the Apache Fluss website to Inter. The goal is to improve the readability of technical documentation and blogs across all devices (Desktop & Mobile) and to provide a more modern, clean visual aesthetic.

Motivation & Rationale
After evaluating several options for technical documentation sites, we chose Inter for the following reasons:

1. Superior Legibility: Inter is specifically designed for computer screens. It features a tall x-height, which makes text highly readable at small sizes and on mobile displays.
2. Neutral & Professional: As a data infrastructure project, our website should look rigorous and clean. Inter offers a "neutral" personality that doesn't distract the reader, similar to the design language used by Vercel, Tailwind CSS, and VitePress.
3. Modern Standard: It has become a de-facto standard in the open-source community for its clarity and extensive character support.

Brief change log

• Updated the global CSS font-family stack.
• Added Inter as the primary sans-serif font.
• Implemented a "System-First" fallback strategy to ensure fast loading and native rendering if web fonts fail to load (e.g., falling back to -apple-system, Segoe UI, etc.).

Screenshots (Before vs. After)**

• Docs Before:

• Docs After:

• Blog Before:

• Blog After:

API and Format

Documentation

[wuchong]

cc @polyzos @MehulBatra , what do you think about this?

[wuchong]

I will merge this for now. We can continue discuss this here.