Clean up public extension documentation

[ascendho]

What changed

• replace retired Marketplace statistics badges with stable Marketplace and GitHub Release badges
• remove RepoRecall migration copy from public READMEs while preserving compatibility code
• translate the Marketplace publishing guide into Chinese and remove obsolete migration instructions
• clarify in the extension manifest that ThreadRelink is a VS Code extension
• assert the public extension description in the manifest test

Why

The old dynamic Marketplace badges now render as retired, legacy migration copy is no longer needed in public-facing documentation, and the Marketplace About text should clearly identify the product as a VS Code extension.

Privacy

Tracked files and the packaged VSIX were scanned for credentials, personal paths, personal email addresses, and real Azure identifiers. No such data was found. Existing Git history is unchanged; this commit uses the GitHub noreply address for future privacy.

Validation

• npx --yes pnpm@10.13.1 check
• npx --yes pnpm@10.13.1 package:vscode
• 27 tests passed
• both replacement badge URLs returned HTTP 200
• public-document and VSIX privacy scans passed
• git diff --check