docs: overhaul README for first-time users

[roonakyadav]

What changed

Restructures the README around first-time visitor needs without removing the important technical documentation.

• Reframes Axonel as a control plane around existing coding agents
• Moves the core workflow and value proposition above deep technical detail
• Adds a clearer "Why Axonel?" section
• Makes the quickstart the primary path after the introduction
• Consolidates the feature tour and documentation into easier-to-scan sections
• Makes the security boundary explicit
• Keeps the existing screenshots and detailed documentation links
• Adds a dynamic GitHub stars badge

This is a documentation-only change; no application code is modified.

[chatgpt-codex-connector]

You have reached your Codex usage limits for code reviews. You can see your limits in the Codex usage dashboard.
To continue using code reviews, you can upgrade your account or add credits to your account and enable them for code reviews in your settings.