docs(website): make Chinese copy more natural

[lucaslus]

What changed

• rewrote the Chinese homepage copy in a more conversational, plain-language tone
• replaced mixed English product jargon such as Todo, Doing, DDL, Notes, AI Agent, and Universal with natural Chinese wording
• aligned the hero demo, metadata, FAQ, footer, and Chinese changelog with the same voice

Why

The current Chinese page reads like a direct translation and makes simple product features sound abstract. This update explains what Floatick does using familiar words and shorter sentences.

Impact

English copy and product behavior are unchanged. The Chinese homepage and changelog become easier to scan and understand.

Validation

• inspected the live Chinese site before editing
• checked the updated homepage and changelog in the local Astro dev server
• verified desktop and 390 px mobile layouts with no horizontal text overflow
• expanded the deadline FAQ and confirmed the answer renders correctly
• confirmed there are no new console errors
• ran git diff --check