docs: add sponsor section to README

[yanglbme]

Summary

• Add a Sponsor section to README.md and README_EN.md, placed right after the introduction
• Feature sponsor APINEBULA in a <table> layout (150px logo + description with referral link), following the style of farion1231/cc-switch so new sponsors can be appended as extra <tr> rows
• Add a "Want to appear here?" call-to-action below the table with WeChat contact (YLB0109) to invite more sponsors

Test plan

• Verify the sponsor section renders correctly on GitHub (logo, links, table layout)
• Confirm npx prettier --check README.md README_EN.md passes (lint-staged hook also ran on commit)
• Check the EN translation reads naturally and the referral link/promo code "leetcode" work as expected

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[Copilot]

Pull request overview

This PR adds a sponsor showcase section near the top of the project’s primary Chinese and English README files, making sponsorship information visible immediately after the introduction.

Changes:

• Add a new Sponsor/赞助商 section after the introduction in both README.md and README_EN.md
• Present APINEBULA as a sponsor using an HTML <table> layout with logo and description/referral link
• Add a short call-to-action inviting additional sponsors to contact via WeChat

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
README.md	Adds a Chinese “赞助商” section with APINEBULA sponsor table and CTA.
README_EN.md	Adds an English “Sponsor” section with APINEBULA sponsor table and CTA.

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