docs(i18n): sync zh-CN README with current main

[ltianyi992]

Summary

The i18n/README.zh-CN.md was significantly out of date with the current README.md. This PR syncs it with the following changes:

• Title: updated from "Context7 MCP" → "Context7 平台 (Platform)"
• Installation: replaced the old per-client JSON config blocks (Cursor / Claude Code / Opencode / OAuth) with the new single-command npx ctx7 setup approach
• Two modes: added the "CLI + Skills" vs "MCP" description that was missing
• Prompt examples: added the third Supabase example; removed the now-outdated inline instruction about appending 用context7
• Tips order: reordered to match main (Use Library Id → Specify a Version → Add a Rule); updated "Add a Rule" copy to mention ctx7 setup
• Available Tools: added the new CLI Commands subsection (ctx7 library / ctx7 docs)
• More Documentation: added the CLI Reference link; renamed "更多MCP客户端" → "MCP客户端"
• Bug fix: corrected the MIT license badge path from ./LICENSE → ../LICENSE (the file lives in i18n/, so the relative path was broken)

Test plan

• Render the Markdown and confirm all badge links, internal anchor links, and external links resolve correctly
• Verify the npx ctx7 setup install command matches the current CLI behavior
• Spot-check Chinese translations for accuracy