Copy Sifta?

Build me a Productivity web app like Sifta.

Sifta does: Sifta is an AI agent that lives in your iMessage, cleans up your inbox automatically, removes spam and noise, and sends summaries of the emails that actually matter. It reportedly makes about $49/mo, so the core idea clearly has demand — I want a lean version I can run and charge for.

Start from the open-source project iOfficeAI/AionUi (https://github.com/iOfficeAI/AionUi) — reuse what fits, strip its branding, and build the specifics below on top of it.

Requirements:
- A chat UI (streaming responses) wired to an LLM with a system prompt you can edit.
- Knowledge base: upload docs/URLs, embed them, and answer from that context (RAG).
- Multi-conversation history, saved prompts, and a shareable/embeddable widget.
- Usage limits per plan and an admin view of conversations.

Also:
- Clean, modern, responsive UI with a thoughtful landing page.
- Email/password auth and a simple paid tier (Stripe test mode) so it's ready to charge.
- A README covering setup, environment variables, and how to deploy.

Ship a working MVP I can run locally first, then help me deploy it.