Stability checkpoint Python — icons + SLO + 5 ADRs + LICENSE

Achievements vs stable-py-v0.6.0 :
- Blue homogeneous icon (radar arcs were yellow → match Python blue)
- README rewrite : hiring TL;DR + SLO badge + Sloth in tech stack
- 3 SLOs as code (Sloth) : availability 99% / latency p99 / enrichment 99.5%
- Generated PrometheusRule + Sloth wrap-as-prometheusrule.py script
- 5 new ADRs : 0008 async-first, 0009 uv, 0010 SQLAlchemy async, 0011 hypothesis, 0012 Sloth SLO
- BSD-3-Clause LICENSE
- TASKS.md SLO + README polish backlog refreshed

Validation : main pipeline #81 green
- ruff:lint + mypy + import-linter ✓
- unit-tests 127 passing, cov 90.21% ✓
- pip-audit clean ✓
- benchmarks (allow_failure ; 6 hot paths run)
- integration-tests (allow_failure ; testcontainers)