Docs: Update Quickstart & Architecture for Multi-Project Platform

[LindungiLw]

• Update lodexi-docs/quickstart.md to reflect the new Multi-Project (Bot) architecture. Clarify that API Keys are scoped per Project, not per User.
• Add a new section in the documentation for Webhook Integrations (How to connect Lodexi to Google Chat/WhatsApp via the Portal's webhook endpoints).
• Add documentation on how to configure the AI Persona / Custom System Prompt.
• Update lodexi-docs/README.md and ARCHITECTURE.md to clearly state that Lodexi is a Multi-Tenant, Multi-Project AI Bot Builder.

Affected Files:

1. lodexi-docs/quickstart.md
2. lodexi-docs/README.md
3. lodexi-docs/ARCHITECTURE.md