docs: Rewrite README.md with professional technical focus

Completely rewrote README.md to be more professional, technical, and modest:

## Changes
- Removed all emojis and marketing language
- Focused on technical accuracy and clarity
- Restructured content for better readability
- Removed percentage-based status indicators
- Made language more modest and precise

## Structure
- Clear overview of language characteristics
- Straightforward build and usage instructions
- Technical examples without excessive commentary
- Honest development status without hype
- Professional tone throughout

## Content Updates
- Simplified feature descriptions
- Focused on implemented functionality
- Removed subjective assessments ("complete", "working", etc.)
- Made performance metrics factual rather than promotional
- Clarified standard library modules (15 modules listed)

The new README presents Cure as a research/educational dependently-typed
language for the BEAM without overstating capabilities or using marketing
terminology.

Co-Authored-By: Warp <agent@warp.dev>

Author: am-kantox