Include Launchplane addons in runtime stack path

[cbusillo]

Summary

• add /opt/launchplane/addons to the shared Odoo runtime stack addon path
• document that startup/config/wrapper paths must agree on the Launchplane runtime-health addon root
• update runtime and IDE tests so generated ODOO_ADDONS_PATH includes the Launchplane addon root

Validation

• git diff --check
• uv run python -m unittest tests.test_ide_support tests.test_runtime.RuntimeCommandTests.test_native_runtime_select_writes_runtime_env_and_pycharm_conf tests.test_runtime.RuntimeCommandTests.test_native_runtime_select_prefers_manifest_mounts_over_runtime_repo_defaults
• uv run ruff check README.md platform/stack.toml tests/test_ide_support.py tests/test_runtime.py

Context

OPW target replacement injects Launchplane runtime identity but /launchplane/health still returns 404. The enterprise image now preserves the base addon path, but devkit still rendered ODOO_ADDONS_PATH from platform/stack.toml without /opt/launchplane/addons, so startup-generated Odoo config could hide the health addon at runtime.