docs: add privacy policy for Chrome Web Store

Author: 11me

PRIVACY.md

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+# Privacy Policy
+
+**LightSession for ChatGPT** is a privacy-first browser extension. This policy explains what data the extension accesses and how it is handled.
+
+## Data Collection
+
+**We do not collect any data.**
+
+LightSession operates entirely locally in your browser. It does not:
+
+- Collect personal information
+- Track your browsing activity
+- Send data to external servers
+- Use analytics or telemetry
+- Store conversation content
+
+## Permissions Explained
+
+| Permission | Purpose |
+|------------|---------|
+| `storage` | Saves your preferences (message limit, UI settings) locally in your browser |
+| `tabs` | Detects when you navigate to ChatGPT to apply settings |
+| Host permissions (`chatgpt.com`, `chat.openai.com`) | Required to inject the performance optimization script on ChatGPT pages |
+
+## How It Works
+
+LightSession intercepts ChatGPT's API responses **locally in your browser** and trims the conversation data before React renders it. This keeps the UI fast without modifying your actual conversation on OpenAI's servers.
+
+All processing happens entirely within your browser. No data ever leaves your device.
+
+## Third Parties
+
+This extension does not share any data with third parties because it does not collect any data.
+
+## Open Source
+
+LightSession is open source. You can review the code at:
+https://github.com/11me/light-session
+
+## Contact
+
+For privacy questions, open an issue on GitHub.
+
+---
+
+*Last updated: January 2026*