Refactor documentation: Fix lists, nav, formatting and duplicates

[PythonWoods]

• docs/conf.py: Enabled advanced navigation (indexes, top, sections) and reformatted.
• docs/index.rst: Simplified landing page and updated Next Steps.
• docs/_snippets: Updated plugin/module lists.
• docs/modules/index.rst: Renamed title.
• docs/guides/user_tutorial.rst: Added core module links.
• packages/.../interfaces.py: Refactored docstrings to fix duplicate object warnings.
• .github/workflows/deploy-docs.yml: Added PR trigger.

Description

Clear description of changes

Type of Change

• Bug fix (non-breaking change fixing an issue)
• New feature (non-breaking change adding functionality)
• Breaking change (fix or feature causing existing functionality to change)
• Documentation update
• Refactoring (no functional changes)

Plugin Checklist (if applicable)

• Protocol interface in src/core/structum/
• Implementation in src/plugins/
• Configuration-driven (no hardcoded values)
• Metrics emission via get_metrics()
• Structured logging via get_logger()
• Health checks implemented
• Graceful shutdown handling
• Documentation added/updated
• Demo application updated

Quality Gates

• Code follows project style (black, ruff)
• Type hints added (mypy --strict passes)
• Tests added/updated (coverage >90%)
• All tests pass locally
• Documentation updated
• CHANGELOG.md updated

Testing

How has this been tested?

# Commands used for testing
pytest tests/test_...py -v

Screenshots (if applicable)

For UI/CLI changes

Breaking Changes

List any breaking changes and migration path

Related Issues

Closes #(issue number)

Checklist

• My code follows the contribution guidelines
• I have performed a self-review
• I have commented complex/hard-to-understand areas
• My changes generate no new warnings
• I have updated the documentation
• I have added tests
• All tests pass
• I have updated CHANGELOG.md