chore: finalize late-0.7 release cleanup

[rlippmann]

What changed

• scoped aggregate coverage reporting to package sources (src/context_compiler) to remove misleading host_support 0% artifact in full coverage runs
• added tiny defensive tests for helper surfaces:
  • observability fallback/transition edge cases
  • confirmation helper fallback paths
  • OpenWebUI show state exact-match normalization (strip().lower())
• aligned LiteLLM integration README checkpoint minimum version wording with 0.7.0
• bumped package version metadata for release:
  • pyproject.toml: version = "0.7.0"
  • uv.lock: editable context-compiler entry to 0.7.0

Why

• improve release-facing coverage signal quality without expanding coverage gates
• harden small helper behaviors that are easy to regress and user/integration visible
• remove stale pre-0.7 docs wording in integration guidance
• ensure release metadata in project/config files matches the 0.7.0 release target

Checklist

• pre-commit run (uv run pre-commit run --all-files)
• tests pass (uv run pytest)