docs: update README with maintainer info and improved scope

[Kedae]

Summary

Updates the README to include maintainer information and document the recent improved scope of the project.

Changes

• Added Maintainer section — Adrien Servel (VP of Software Engineering) listed as the project maintainer
• Added Recent Improvements section — Documents the latest improvements including electric button theme, bot greeting update, proxy server security, custom CSS support, and responsive design enhancements
• Updated project title — Changed from "Flowise Embed" to "Filigran Chatbox" to reflect the project's identity
• Fixed minor formatting — Added missing comma in the form config example

Source

From the Chatbox Improvement brainstorm — Chunk 1 of 3.