docs: redesign README with hero graphic and zh-CN version

[rcyw]

Summary

• Redesign README around a project-native SVG hero: title plus a five-stage job lifecycle strip (submit → admit → build → push → preheat) drawn from the real service build flow.
• Restructure the README to value → quick start → mechanism (Why Kova) → docs → develop; no behavior or command changes.
• Add README.zh-CN.md with an English | 中文 switcher.
• Update .x/development.md: drop rules duplicated in AGENTS.md, and replace the 80-column wrap rule with one-sentence-per-line (English) / one-paragraph-per-line with fullwidth punctuation (Chinese).

Validation

• make docs-check (27 Markdown files)
• git diff --check
• SVG audited (local image refs, title/desc, no script/foreignObject) and previewed at 900px and 360px widths