Restore supported local runtime config resolution

[cbusillo]

Summary

• replace the retired checkout/file runtime-environment lookup with one typed ODOO_DEVKIT_RUNTIME_ENVIRONMENT_JSON boundary
• enforce exact context/instance scope, safe env names/values, stack-required nonblank values, and final publish/runtime revalidation
• scrub payload secrets from internal child processes and remove supported Compose .env fallback
• update static and generated workspace guidance for operator-local setup while preserving Launchplane ownership of non-local mutation and artifact payload injection

Validation

• uv run python -m unittest discover -s tests — 169 tests passed, 1 skipped
• uv run ruff format --check .
• uv run ruff check .
• uv build
• uv run platform --help
• live platform workspace sync, local runtime inspect, and runtime select proof
• Docker Compose config --quiet against the generated runtime env
• proof values absent from runtime inspect output
• changed-file PyCharm inspection — GREEN, 0 findings
• independent multi-agent review, including follow-up validation of all findings

Closes #78