docs: add multilingual README landing - #46

Summary

• Add README language navigation for seven languages
• Add release, Python, license, ADR locale, and README language badges
• Add translated README variants under docs/readme to keep the repository root uncluttered
• Record the documentation change in changelog.md

Verification

• uv run --python 3.12 --extra dev python -m pytest tests/unit tests/integration -v --cov=skills/adr-toolkit/scripts --cov-branch --cov-report=term-missing --cov-fail-under=85
• uv run --python 3.12 --extra dev ruff check .
• uv run --python 3.12 --extra dev mypy skills/adr-toolkit/scripts/core/atomic_io.py skills/adr-toolkit/scripts/core/telemetry.py skills/adr-toolkit/scripts/core/contracts.py --strict
• uv run --python 3.12 python scripts/sync_version.py --check
• uv run --python 3.12 python scripts/verify_examples.py --check