- LEXAI-13: TweetNaCl secretbox encryption for API keys in Options + background
- getOrCreateEncKey() generates per-device 32-byte key stored in chrome.storage.local
- Keys saved as nonce+ciphertext (base64) under apiKeyEnc
- Backward compat: falls back to plaintext apiKey if no encrypted key found
- Lock icon 🔒 shown in Options label when key is encrypted
- LEXAI-11: Right-click context menu with Fix, Rephrase, Shorten, Expand, Tone
- Registered via onInstalled in background service worker
- Sends lexai-context-menu message to content script
- Content script listener added at bottom of main()
- LEXAI-12: Tone analysis button added to floating toolbar (teal #2dd4bf)
- Analysis-only: showModal called with null originalText = no Replace button
- Tone system prompt updated to pure analysis (no rewrite)
