v1.13.0 - Gold quality scale milestone

Gold

The integration now declares quality_scale: gold in its manifest. Every required Gold-tier rule of the Home Assistant integration quality scale is satisfied — see custom_components/eaux_marseille/quality_scale.yaml for the per-rule breakdown. The remaining todo is strict-typing (Platinum), already passing locally with mypy strict but pending the official HA strict-typing CI hook opt-in.

CONTRIBUTING.md

New top-level guide (~80 lines) for contributors. Documents:

• Two paths for running tests locally:
  • Quick path — minimal install (pytest + aioresponses + tenacity); exercises all HA-independent code paths via the MagicMock fallback in tests/conftest.py. Tests marked @pytest.mark.ha_required skip cleanly.
  • Full path — pip install -r requirements_test.txt pulls Home Assistant core and ~100 transitive deps (~450 MB). Required to see all 49 tests pass and mirror what CI runs.
• The five quality gates (ruff lint, ruff format, mypy strict, pytest, hassfest+HACS) with their local commands.
• Code conventions (short modules, defensive parsing on portal payloads, type-ignore / noqa policy).
• Commit-message and release procedure.

The README's Contributing section now points to CONTRIBUTING.md with a quick checklist.

What didn't change

No code touched. No behaviour change for users. This release is the milestone marker for the quality-scale promotion + the contributor-onboarding guide that should have shipped alongside the Silver→Gold work.

Verified

• All 5 CI jobs green
• Local validation clean (ruff, mypy strict, pytest)

Closes #16.