Stability checkpoint v0.4 — Python 3.14 + mkdocs autodoc + Pages

- Python 3.13 → 3.14 (latest GA, oct 2025)
- Pydantic 2.11 (3.14 wheel support)
- ruff 0.15 (py314 target) + mypy 1.20
- Drop Py3.11 from compat matrix (EOL Oct 2027)
- mkdocs-material doc site + autodoc via mkdocstrings
- GitLab Pages CI publishes https://mirador1.gitlab.io/mirador-service-python/

Quality : 95 tests · ruff ✅ · mypy strict ✅ · coverage 83.77 %.