fix: Remove or implement broken validate-streamlit command

[db-tycoon-stephen]

Problem

validate-streamlit is registered in pyproject.toml but the underlying script doesn't exist. Running uv run validate-streamlit will crash with ImportError.

The src/web/ directory is completely empty (subdirectories exist but contain no Python files).

Proposed Solution

Remove all broken web/Streamlit commands from pyproject.toml and management_cli.py:

• validate-streamlit
• Any references to web or deploy-streamlit in help text

Add a placeholder issue for future Streamlit implementation.

Acceptance Criteria

• No broken commands in pyproject.toml
• All registered commands respond to --help without errors
• Empty src/web/ directories cleaned up or documented