docs: make README blunt and restore original badges

[henryoman]

Motivation

• Simplify the top-level README to present a blunt, user-facing description and reduce developer-focused noise.
• Restore the runtime/stack badges the maintainer preferred so the project identity and stack are visible at a glance.
• Provide minimal, actionable install/run/update instructions for end users using a placeholder package name.
• Keep a short contributor section so running from source remains possible without dominating the page.

Description

• Rewrote the README copy to a concise, blunt tagline and short user-focused sections (Install, Run, Update, Troubleshooting).
• Restored the original badges for Bun, TypeScript, OpenTUI, Convex, Better Auth, and status at the top of the file.
• Replaced the developer-heavy Quick Start and environment setup steps with a compact contributor section that lists bun install, bun run convex:dev, and bun dev.
• Kept the placeholder package name chui-cli for npm/Homebrew install and update instructions and kept troubleshooting guidance minimal.

Testing

• Verified the updated file contents with sed -n '1,220p' README.md, which completed successfully.
• Reviewed the formatted file with nl -ba README.md, which completed successfully.
• Confirmed the working tree status with git status --short, which reported the repository state successfully.

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Codex Task