Fix inherited rollback plan availability

[shiny-code-bot]

Summary

• resolve inherited generic-web rollback-plan availability against the prod lane
• require a prod lane before advertising the inherited rollback planner as supported
• cover Odoo inherited rollback-plan context and missing-prod-lane behavior in product read-model tests

Validation

• uv run python -m unittest tests.test_product_environment_read_model tests.test_driver_descriptors
• uv run --extra dev ruff check --diff control_plane/contracts/product_environment_read_model.py tests/test_product_environment_read_model.py
• uv run --extra dev ruff check control_plane/contracts/product_environment_read_model.py tests/test_product_environment_read_model.py
• uv run --extra dev ruff format --check control_plane/contracts/product_environment_read_model.py tests/test_product_environment_read_model.py
• uv run --extra dev mypy control_plane tests

Notes

• JetBrains inspection returned only STATUS: error; no actionable findings were available from the tool.
• One read-only planning agent was still running; the completed agents plus local audit were enough for this narrow correctness fix.