Add Python quality gates and modular validators

[Codewriter90x]

Summary

• add Ruff, mypy and coverage gates with pinned development dependencies
• validate Python 3.11, 3.12 and 3.13 while preserving the required Data quality gate
• split dataset validation into schema, territory, coordinate, provenance and format modules

Verification

• Ruff: passed
• mypy: passed (8 source files)
• coverage: 78%, threshold 75%
• Python unittest: 39 passed
• Node Pages tests: 6 passed
• deterministic build, Pages build and release validation: passed