chore(chat): rebuild context with security + sandbox docs pages

11 docs pages (was 9), 80824 bytes (~20206 tokens). New pages:
- /docs/security (Security Model)
- /docs/sandbox (Sandbox overview)
- /docs/sandbox/just-bash (just-bash integration)

Worker deployed to speckit-security-chat.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: kaman1