docs(legal): add privacy policy (PRIVACY-POLICY.md)

Author: StringNick

PRIVACY-POLICY.md

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+# Privacy Policy for DecaNotes
+
+Last updated: October 29, 2025
+
+## Overview
+DecaNotes is a decentralized note-taking application that prioritizes your privacy and data ownership.
+
+## Data Collection
+DecaNotes does NOT collect, store, or transmit any personal data to our servers. We do not have servers.
+
+## Data Storage
+- **Local Storage**: Notes are stored only on your device
+- **Sia Renterd**: If you choose this option, notes are encrypted and stored on the Sia decentralized network using your own credentials
+- **IPFS**: If you choose this option, notes are stored on the IPFS network using your configuration
+
+## Data Security
+All data stored through DecaNotes is under your complete control:
+- Local storage uses your device's secure storage
+- Decentralized storage options (Sia, IPFS) use your own encryption keys and credentials
+- We never have access to your notes or credentials
+
+## Third-Party Services
+When you use decentralized storage options (Sia or IPFS), you connect directly to those networks. Please review their respective privacy policies:
+- Sia Network: https://sia.tech
+- IPFS: https://ipfs.tech
+
+## Analytics and Tracking
+We do not use any analytics, tracking, or telemetry services. Your usage of DecaNotes is completely private.
+
+## Children's Privacy
+DecaNotes does not knowingly collect any information from children under 13 years of age.
+
+## Changes to This Policy
+We may update this Privacy Policy from time to time. We will notify users of any changes by updating the "Last updated" date.
+
+## Contact
+For questions about privacy, please open an issue at: https://github.com/StringNick/decanotes/issues
+
+## Your Rights
+Since we do not collect any data, there is no data to access, modify, or delete. You have complete control over all your notes stored locally or on decentralized networks.