Add AI prompt snippets plugin

[sarathkumar1207]

Summary

• add an AI Prompt Snippets plugin with reusable commands for common Cursor AI workflows
• include commands for code explanation, code review, test generation, readability refactors, and documentation
• register the plugin in the marketplace manifest and README

Validation

• node scripts/validate-plugins.mjs

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Note

Low Risk
Additive plugin content and manifest/README entries only; no changes to auth, data handling, or shared validation logic beyond the new marketplace entry.

Overview
Introduces a new ai-prompt-snippets Cursor plugin and lists it in .cursor-plugin/marketplace.json and the root README.md plugins table.

The plugin ships five palette commands (explain, review, write tests, refactor for readability, generate docs) as markdown command definitions under commands/, plus a prompt-snippets agent skill. Packaging follows the usual plugin layout: plugin.json, MIT license, changelog, README, and logo asset—no application or marketplace runtime code changes beyond registration.

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