docs: add privacy policy for AMO listing

Required for Firefox Add-ons (AMO) public listing submission.
Documents that all processing is 100% local, no data collection,
no servers, no analytics. Explains each permission and all
optional network requests (sync, org policy).

https://claude.ai/code/session_01SWSwDfMVij53bCTNSCLMwn

PRIVACY.md

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+# Privacy Policy — Silent Send
+
+**Last updated:** March 26, 2026
+
+## Summary
+
+Silent Send does not collect, transmit, or store any data externally. All processing happens 100% locally in your browser. There are no servers, no analytics, no tracking, and no telemetry of any kind.
+
+## What data Silent Send accesses
+
+Silent Send accesses the following data **only within your browser** to perform its core function (substituting personal information before it reaches AI services):
+
+- **Text you type** in AI chat interfaces (Claude, ChatGPT, Grok, Gemini, etc.) — scanned for configured personal information and substituted before sending
+- **Files you upload** to AI services — text is extracted and scanned for personal information before upload
+- **Your identity configuration** — names, emails, usernames, hostnames, phones, and their substitute values, stored in browser local storage
+- **Your substitution mappings** — real-to-substitute value pairs you configure
+- **Activity log** — a local record of substitutions performed (never sent anywhere)
+- **Settings and preferences** — extension configuration
+
+## Where data is stored
+
+All data is stored in your browser's `storage.local` (the extension's private storage area). When at-rest encryption is enabled, all sensitive data is AES-256-GCM encrypted before being written to storage.
+
+Data is **never** sent to any server operated by Silent Send or any third party. The only network requests Silent Send makes are:
+
+- **To the AI service you are already using** (e.g., claude.ai, chatgpt.com) — this is the substituted/sanitized version of your text, not the original
+- **GitHub Gist sync** (optional, user-initiated) — if you configure Gist sync, your encrypted settings are stored in a private Gist on your own GitHub account
+- **Custom URL sync** (optional, user-initiated) — if you configure a custom sync endpoint, encrypted settings are sent to the URL you specify
+- **Org policy URL** (optional) — if you join an organization, the extension fetches the policy JSON from the URL your admin provides
+
+## Data sharing
+
+Silent Send does not share any data with anyone. There are no analytics providers, no crash reporting services, no advertising networks, and no data brokers involved.
+
+## Data retention
+
+All data persists in your browser until you delete it. You can:
+- Clear all data via Options → Danger Zone → Reset Everything
+- Uninstall the extension (removes all stored data)
+- Export your data before clearing
+
+## Permissions explained
+
+| Permission | Why it's needed |
+|---|---|
+| `storage` | Store your identity, mappings, settings, and activity log locally |
+| `activeTab` | Access the current tab to inject the substitution script |
+| `scripting` | Inject content scripts on custom domains you configure |
+| `notifications` | Show desktop notifications for sync status updates |
+| `alarms` | Background polling for auto-sync and org policy updates |
+| Host permissions (claude.ai, etc.) | Intercept API requests to substitute personal information before sending |
+
+## Children's privacy
+
+Silent Send does not knowingly collect data from children under 13. The extension does not collect data from anyone — it processes everything locally.
+
+## Changes to this policy
+
+If this privacy policy changes, the updated version will be posted at this URL and in the extension's GitHub repository.
+
+## Contact
+
+For questions about this privacy policy, open an issue at: https://github.com/outis1one/silent-send/issues
+
+## Open source
+
+Silent Send's source code is publicly available at https://github.com/outis1one/silent-send — you can verify every claim in this policy by reading the code.