Docs: Add problem-first introduction to README

[KalkurV]

Description

This PR adds a short "The Problem Hive Solves" section at the top of the README to help first-time visitors quickly understand why Hive exists before diving into technical details.

The goal is to improve first-time comprehension, reduce cognitive load, and create a clearer entry point for users evaluating the project.

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)

Related Issues

Fixes #3223

Changes Made

• Added a problem-first narrative section at the very top of README
• Framed Hive’s purpose before introducing capabilities
• Improved entry experience for new users

Testing

Describe the tests you ran to verify your changes:

• Unit tests pass (cd core && pytest tests/)
• Lint passes (cd core && ruff check .)
• Manual review of README rendering and structure

Checklist

• I have performed a self-review of my changes
• I have made corresponding changes to the documentation

Screenshots (if applicable)

N/A – Documentation change