[michalmaj]

Summary

Add strict local type checking with mypy and introduce static typing as the first topic after the original project foundation.

Why

The example code already uses type hints, but annotations do not check themselves. This change gives readers a focused explanation of static type checking before it becomes part of the automated CI workflow.

Changes

• add mypy as a locked development dependency
• configure strict Python 3.12 checking for src/ and tests/
• add a type-checking chapter and connect it to the main learning path
• update project configuration, glossary, common questions, and roadmap references

Type of change

Select the most relevant option.

• Documentation
• Project configuration
• New feature
• Tests
• CI/CD
• Refactoring
• Bug fix

Checklist

• The change is small and focused
• The pull request title is clear
• I updated documentation if needed
• I added or updated tests if needed
• I ran local checks if applicable

Notes

The mypy configuration uses strict = true. The current codebase passes without
ignores or per-module exceptions.

CI integration is intentionally left for the follow-up 7B pull request so this
change can focus on the tool, configuration, and learning material.

Local checks passed:

• uv run mypy
• uv run ruff check .
• uv run ruff format --check .
• uv run pytest
• uv build --no-sources
• git diff --check