docs: overhaul README for clarity and modern design

[Kubaguette]

Description

This PR drastically improves the readability, flow, and visual structure of our README.md to ensure a better onboarding experience for new users.

Key changes:

• Modernized "Why EnvStation?": Rewrote the value proposition to directly address the "split-brain" container problem on immutable distributions. Implemented a clean, progressive disclosure design using <details> and <blockquote> tags to keep the main view uncluttered while preserving technical depth.
• Streamlined "Quick Start": Removed the deprecated AppImage references and condensed the installation guide into scannable, easy-to-read code blocks.
• General Polish: Removed "walls of text" while maintaining necessary information.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring / Documentation update

Architecture Checklist:

• My code follows the ARCHITECTURE.md guidelines.
• I have routed system commands through the Host-Executor (build_host_command_async) where necessary. (N/A - Docs only)
• I have performed a self-review of my own code.