Add AgoraIO organization profile README

[plutoless]

Summary

• replace the decorative Banner with a restrained developer-focused brand asset
• remove the three synthetic Showcase illustrations
• use GitHub-native headings, code blocks, links, and tables for detailed content
• add one authentic Voice AI Recipes viewport capture as product evidence
• retain verified Skills/CLI commands, recipe shortcuts, Server SDKs, and RTE examples

Validation

• validated the Banner SVG with xmllint
• verified the Recipes screenshot format and dimensions
• checked required and removed README content
• reviewed GitHub rendering in light, dark, and 390px narrow views
• verified recipe, repository, docs, website, social, badge, and Discord destinations
• confirmed remote main still has no profile/README.md

Publishing behavior

Merging this PR will publish profile/README.md on the public AgoraIO organization homepage.