Improve README overview and usage

[fazpu]

Summary

• Rework README around loopy-loop's value proposition and PyPI-based install flow
• Add skill setup, inner_outer_eval initialization, and goal editing guidance
• Add high-level architecture plus deeper configuration, logging, control, workflow, and HTTP contract explanations

Validation

• uv build
• uv run --with twine twine check --strict dist/*
• uv run ruff check src/
• uv run ruff format --check src/
• uv run pyright src/ --pythonversion 3.13
• uv run pytest src/tests/ -v --tb=short