Rewrite README as project landing page

[dcellison]

Summary

Rewrites the README as a shorter project landing page for Kai's current positioning as a local, Telegram-first personal engineering system.

Changes

• Leads with the personal engineering system framing and the practical value of reaching a local agent from Telegram.
• Compresses architecture, security, backend, workflow, and setup content into a front-page overview.
• Moves detailed operational material toward the wiki by linking to the relevant pages instead of embedding long reference sections.
• Removes the full command table, environment variable table, service setup examples, project tree, and protected-install manual from the README.

Verification

• Ran git diff --check.
• Checked the rewritten README for em dash and en dash characters.
• Checked the rewritten README for personal/local-only references.