Extract product config service route

[cbusillo]

Summary

• move product-config apply/plan HTTP request validation and response handling into control_plane/product_config_http.py
• keep service.py responsible for idempotency and app wiring while product-config route details live with the product-config boundary
• reduce control_plane/service.py to 7,633 lines in this slice

Refs #307

Validation

• uv run python -m unittest tests.test_service.LaunchplaneServiceTests.test_product_config_api_dry_run_returns_redacted_plan_without_writes tests.test_service.LaunchplaneServiceTests.test_product_config_api_apply_writes_runtime_and_managed_secret tests.test_service.LaunchplaneServiceTests.test_product_config_api_rejects_missing_master_key_for_secret_bundle tests.test_service.LaunchplaneServiceTests.test_product_config_api_requires_runtime_key_safety_policy tests.test_service.LaunchplaneServiceTests.test_product_config_api_rejects_secret_shaped_runtime_key tests.test_service.LaunchplaneServiceTests.test_product_config_api_apply_requires_apply_authorization tests.test_service.LaunchplaneServiceTests.test_product_config_api_rejects_unauthorized_context tests.test_service.LaunchplaneServiceTests.test_product_config_api_rejects_runtime_env_target_override tests.test_service.LaunchplaneServiceTests.test_product_config_api_rejects_secret_scope_override tests.test_service.LaunchplaneServiceTests.test_product_config_api_rejects_secret_target_override tests.test_product_config_service
• uv run --extra dev ruff check --diff control_plane/service.py control_plane/product_config_http.py
• uv run --extra dev ruff check control_plane/service.py control_plane/product_config_http.py
• uv run --extra dev mypy control_plane/service.py control_plane/product_config_http.py