Add Sauna Care & Performance Kit (inspection, UV‑C, maintenance)

[chrbailey]

Motivation

• Provide a deployable, safety‑first maintenance and performance specification for traditional electric saunas to address the requested facilities deliverable.
• Prevent unsafe ad‑hoc heater modifications (glass door, floor, ceiling, portable heaters) by prescribing approved upgrade paths and licensed installation.
• Document inspection, calibrated temperature mapping, cedar/hemlock cleaning and reconditioning, optional interlocked UV‑C sanitation, spares, commissioning, and a maintenance/runbook to support safe deployment.

Description

• Add a comprehensive spec file at docs/SAUNA_CARE_AND_PERFORMANCE_KIT.md covering safety boundaries, kit module contents, calibrated temperature and spot‑check methods, wood care for cedar/hemlock, UV‑C unoccupied‑cycle requirements, spares, and technical commissioning and acceptance checklists.
• Explicitly prohibit improvised supplemental heaters on glass doors, floors, roofs, or ceilings and require listed heaters, manufacturer guidance, and licensed electricians for electrical work.
• Include an approved upgrade path (restore, replace primary heater, or manufacturer‑approved engineered dual‑heater) and a deployment runbook, procurement/sign‑off record, governing‑documents checklist, and recurring maintenance schedule.
• Link the new deliverable from the project README.md so it is discoverable from the repo front page.

Testing

• Ran git diff --check and a small validation script that verified required sections exist and the README.md links to docs/SAUNA_CARE_AND_PERFORMANCE_KIT.md, and both checks passed.
• Executed the full test suite with python -m pytest tests/ -q, resulting in 141 passed tests and pre‑existing deprecation warnings about datetime.utcnow() (no new test failures).
• Confirmed the repo worktree shows the documentation file present and the README updated as intended.

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Codex Task