feat(docs): Create agent.md and docs folder

[mkmeral]

Description

Reorganizes contributor documentation to improve discoverability and consistency with the TypeScript SDK.

Changes:

• Add AGENTS.md at root - guidance for AI agents/LLMs working with the codebase
• Create docs/ folder for contributor documentation
• Move STYLE_GUIDE.md → docs/STYLE_GUIDE.md
• Move _MCP_CLIENT_ARCHITECTURE.md → docs/MCP_CLIENT_ARCHITECTURE.md
• Move src/strands/hooks/rules.md → docs/HOOKS.md (consolidated and expanded)
• Add docs/README.md explaining the folder contents
• Update references in CONTRIBUTING.md

Related Issues

N/A

Documentation PR

N/A - this PR is documentation reorganization within the SDK repo

Type of Change

Documentation update

Testing

No code changes - documentation only.

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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