Improve documentation — user guide, configuration reference, and examples #16

Description

Expand the Sphinx documentation with a comprehensive user guide, a full configuration reference for moduletester.ini, and practical usage examples. The documentation should enable a new user to go from zero to a working test plan without external help.

Current behavior

• Documentation covers basic installation and usage.
• Configuration options are not fully documented.
• No step-by-step tutorial for common workflows.
• No API reference for programmatic usage.

Expected behavior

• User Guide: step-by-step tutorial covering the full workflow (project setup → test discovery → execution → export).
• Configuration Reference: every moduletester.ini option documented with type, default, and example.
• CLI Reference: all command-line arguments and subcommands documented.
• FAQ / Troubleshooting: common issues and solutions.
• Template Customization Guide: how to create custom Jinja2 export templates.
• Integration Guide: how to integrate ModuleTester into an existing Python project.

Acceptance criteria

• User guide with end-to-end workflow tutorial
• Full moduletester.ini configuration reference
• CLI reference for all commands and options
• Template customization guide
• FAQ section with common issues
• Documentation builds without warnings