fix: address telemetry and environment quality findings

[mldangelo-oai]

Summary

• share one global config read across telemetry identity/email initialization
• serialize telemetry singleton construction so shutdown registration happens once
• add coverage for readable probe files and Kubernetes container tuple results

Validation

• uv sync --python 3.14 --extra dev
• uv run python --version (Python 3.14.5)
• uv run ruff check src/ tests/test_telemetry.py tests/test_environment.py
• uv run ruff format --check src/ tests/test_telemetry.py tests/test_environment.py
• uv run mypy src/promptfoo/
• uv run pyright src/promptfoo/
• uv run pytest tests/ -v -m 'not smoke'\n- uv run pytest tests/smoke/ -v\n- uv build