Add privacy policy for extension store submissions

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

PRIVACY_POLICY.md

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+# Privacy Policy
+
+**Plebeian Signer** is a browser extension for managing Nostr identities and signing events. This privacy policy explains how the extension handles your data.
+
+## Data Collection
+
+**Plebeian Signer does not collect, store, or transmit any user data to external servers.**
+
+All data remains on your device under your control.
+
+## Data Storage
+
+The extension stores the following data locally in your browser:
+
+- **Encrypted vault**: Your Nostr private keys, encrypted with your password using Argon2id + AES-256-GCM
+- **Identity metadata**: Display names, profile information you configure
+- **Permissions**: Your allow/deny decisions for websites
+- **Cashu wallet data**: Mint connections and ecash tokens you store
+- **Preferences**: Extension settings (sync mode, reckless mode, etc.)
+
+This data is stored using your browser's built-in storage APIs and never leaves your device unless you enable browser sync (in which case it syncs through your browser's own sync service, not ours).
+
+## External Connections
+
+The extension only makes external network requests in the following cases:
+
+1. **Cashu mints**: When you explicitly add a Cashu mint and perform wallet operations (deposit, send, receive), the extension connects to that mint's URL. You choose which mints to connect to.
+
+2. **No other external connections**: The extension does not connect to any analytics services, tracking pixels, telemetry endpoints, or any servers operated by the developers.
+
+## Third-Party Services
+
+Plebeian Signer does not integrate with any third-party services. The only external services involved are:
+
+- **Cashu mints**: User-configured ecash mints for wallet functionality
+- **Browser sync** (optional): Your browser's native sync service if you enable vault syncing
+
+## Data Sharing
+
+We do not share any data because we do not have access to any data. Your private keys and all extension data remain encrypted on your device.
+
+## Security
+
+- Private keys are encrypted at rest using Argon2id key derivation and AES-256-GCM encryption
+- Keys are never exposed to websites — only signatures are provided
+- The vault locks automatically and requires your password to unlock
+
+## Your Rights
+
+Since all data is stored locally on your device:
+
+- **Access**: View your data anytime in the extension
+- **Delete**: Uninstall the extension or clear browser data to remove all stored data
+- **Export**: Use the extension's export features to backup your data
+
+## Changes to This Policy
+
+Any changes to this privacy policy will be reflected in the extension's repository and release notes.
+
+## Contact
+
+For questions about this privacy policy, please open an issue at the project repository.
+
+---
+
+**Last updated**: January 2026
+
+**Extension**: Plebeian Signer v1.1.5