Redesign sponsor pages and support paths

[brownie-cake]

What changed

• rewrote the English and Chinese sponsor pages around the value File Viewer creates and the maintenance work sponsorship funds
• added clear community sponsorship, domestic one-time support, and enterprise support paths
• added contribution guidance without fixed pricing or paid issue priority
• documented explicit boundaries around SLA, delivery commitments, confidential files, licensing, and feature guarantees
• refreshed the bilingual sponsor landing page and SUPPORT.md
• expanded .github/FUNDING.yml to expose both domestic sponsorship and enterprise support

Why

The previous pages listed payment links but did not clearly explain why ongoing maintenance is expensive, how funds are used, or when an organization should choose a scoped commercial engagement instead of community sponsorship. The new copy is designed to improve trust and conversion while preserving fair public issue handling and the Apache-2.0 open-source commitment.

User impact

Potential sponsors can understand the maintenance value, choose an appropriate support route, and see what sponsorship does and does not include. Enterprise users are directed to a contract-ready path instead of expecting SLA-backed support from a community donation.

Validation

• reviewed the complete branch diff against main
• confirmed only Markdown and .github/FUNDING.yml are changed
• confirmed the existing VitePress sidebars already link to /en/donate and /zh/donate
• no runtime code or package behavior is modified