Implement EnzoBot CLI with intent routing and unit tests

[ReedonMenu]

Motivation

• Replace the previous README-only update with a runnable assistant implementation so the repository contains executable behavior and verifiable outputs.
• Provide a small, deterministic intent router that produces structured, markdown-style responses for common prompt categories to support CLI and programmatic usage.
• Add automated tests to prevent regressions and to validate core response paths.

Description

• Add src/enzobot.py which defines an IntentRule dataclass and an EnzoBot class with regex-based intent rules for greeting, plan, code, and a fallback handler, plus a main() CLI entrypoint.
• Add tests/test_enzobot.py with unit tests that assert behavior for empty input, a code-related prompt, and a general/fallback prompt.
• Update README.md with run instructions and the python3 -m pytest -q command so contributors can run the CLI and tests locally.

Testing

• Ran python3 -m pytest -q and the full test suite succeeded.
• Test output: 3 passed in 0.03s indicating the added tests passed successfully.

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Codex Task