Copy syncdate.app?

Build me a Productivity web app like syncdate.app.

syncdate.app does: SYNCDATE is a two-way calendar sync utility for Google, Outlook, iCloud/CalDAV, and iCal feeds. Connect multiple accounts, pick which calendars sync, and changes propagate in seconds via webhooks. Syn It reportedly makes about $114/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.