chore: prepare 0.8.0 release

[douglasmonsky]

Summary

• bump package, plugin manifest, and MCP runtime pin to 0.8.0
• add 0.8.0 changelog covering Diagnostics, source-offset context seek, and dashboard loading hardening
• update release/development docs and 1.0 readiness public-smoke version references

Local release gate

• PYTHONPATH=src .venv/bin/python -m ruff check .
• PYTHONPATH=src .venv/bin/python -m mypy
• PYTHONPATH=src .venv/bin/python -m pytest
• PYTHONPATH=src .venv/bin/python -m pytest --cov=codex_usage_tracker --cov-report=term-missing
• PYTHONPATH=src .venv/bin/python -m compileall src
• for file in src/codex_usage_tracker/plugin_data/dashboard/dashboard*.js; do node --check ""; done
• PYTHONPATH=src .venv/bin/python scripts/check_release.py
• git diff --check
• rm -rf dist build src/codex_usage_tracker.egg-info src/codex_usage_tracking.egg-info
• .venv/bin/python -m build
• .venv/bin/python -m twine check dist/*
• PYTHONPATH=src .venv/bin/python scripts/check_release.py --dist
• .venv/bin/python scripts/smoke_installed_package.py
• .venv/bin/python scripts/smoke_installed_package.py --docker
• additional safe CLI smoke commands to /tmp outputs

Dist hashes

• wheel: 6a19a66c355f62f772f3b7f6bdde8120ce6c6d484c004cbe41544bc317888853
• sdist: 9855d6b95bda6fbbac921056f278f7dfa278961005c298b82af8f901426e3db2