feat(gateway): accurate status read for apps and components

[bburda]

Summary

Make GET /{apps|components}/{id}/status report ready / notReady from real signals instead of
coarse ones. Read-only; the PUT lifecycle transitions stay 501 (actuation is tracked separately).

• App status: for a managed lifecycle node (one exposing lifecycle_msgs get_state and
  change_state), the status is read from the actual lifecycle state via a GetState service call
  (active is ready; any other state, or an unreachable/timed-out read, is notReady). This
  subsumes liveness, since a dead node's service is gone. Plain (unmanaged) nodes keep using
  App::is_online (presence in the ROS 2 graph), which is the best signal available for an
  unmanaged node.
• Component status: a local component is ready while the gateway is serving the request (the
  substrate is reachable), independent of how many hosted apps are online, including zero. The old
  "at least one hosted app online" rule and the host_metadata special-case are removed. A down
  hosted app is that app's own notReady, not the component's. Remote components are unchanged
  (reached through aggregation forwarding).

The lifecycle read goes through a small injected LifecycleStateReader seam: a pure interface in
gateway_core (keeps the handler unit-testable with a stub and preserves core purity) plus a
gateway_ros2 implementation that calls GetState on a private node and private single-threaded
executor spun inline (mirrors the existing ros2_fault_service_transport pattern, so it never
blocks or races the gateway executor). A managed_lifecycle rclcpp_lifecycle demo node and an
integration test prove the path end to end.

The third LifecycleHandlers constructor parameter is defaulted, so existing call sites and
non-lifecycle apps are unchanged. No API break.

Issue

• closes Accurate status read for apps and components #454

Type

• New feature or tests

Testing

Unit (GTest):

• Pure helpers: active to ready, other state or nullopt to notReady; the lifecycle-service
  detector requires both get_state and change_state.
• Ros2LifecycleStateReader against an in-process GetState service: reads active / inactive,
  returns nullopt for an unreachable service.
• Handler: a managed node whose state is inactive reports notReady even though it is online
  (the discriminator); an active managed node reports ready; a plain node still uses is_online.
  Component reads return ready for the host component, a zero-app component, and a component whose
  hosted apps are all offline.

Integration (launch_testing):

• A managed_lifecycle node is launched and left unconfigured. It is present in the ROS 2 graph
  (so is_online alone would say ready), but GET /apps/managed_lifecycle/status returns
  notReady, proving the status is read from the lifecycle state via GetState. Tagged
  @verifies REQ_INTEROP_076.

clang-tidy is clean on the changed files.

Checklist

• Breaking changes are clearly described (none - additive; the new constructor parameter is defaulted)
• Tests were added or updated if needed
• Docs were updated if behavior or public API changed (design doc + README)

[Copilot]

Pull request overview

This PR makes GET /api/v1/{apps|components}/{id}/status reflect more accurate readiness signals: lifecycle-managed apps report readiness from lifecycle_msgs/srv/GetState, and local components are always ready while the gateway is reachable (remote components still rely on aggregation forwarding).

Changes:

• App status now uses lifecycle state when the app exposes both GetState and ChangeState services (active → ready, otherwise/timeout → notReady), falling back to is_online for unmanaged nodes.
• Component status (no provider) is simplified: any reachable local component returns ready independent of hosted app presence.
• Adds a LifecycleStateReader seam (core interface + ROS2 implementation), plus unit/integration tests and a new lifecycle demo node.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/ros2_medkit_integration_tests/test/features/test_lifecycle.test.py	Adds an integration test proving lifecycle-based status for an unconfigured lifecycle node.
src/ros2_medkit_integration_tests/ros2_medkit_test_utils/launch_helpers.py	Registers the new managed_lifecycle demo node for launch tests.
src/ros2_medkit_integration_tests/package.xml	Adds rclcpp_lifecycle dependency for the new demo node.
src/ros2_medkit_integration_tests/demo_nodes/managed_lifecycle_node.cpp	New lifecycle demo node (defaults to unconfigured) used by integration tests.
src/ros2_medkit_integration_tests/CMakeLists.txt	Builds/installs the managed_lifecycle demo executable and finds rclcpp_lifecycle.
src/ros2_medkit_gateway/include/ros2_medkit_gateway/core/status/lifecycle_state_reader.hpp	Introduces core lifecycle reader interface + helper declarations (core-pure seam).
src/ros2_medkit_gateway/src/core/status/lifecycle_status_helpers.cpp	Implements lifecycle-state → SOVD-status mapping and lifecycle-service detection helper.
src/ros2_medkit_gateway/include/ros2_medkit_gateway/ros2/status/ros2_lifecycle_state_reader.hpp	Declares ROS2 GetState-backed lifecycle reader implementation.
src/ros2_medkit_gateway/src/ros2/status/ros2_lifecycle_state_reader.cpp	Implements lifecycle state reads via a private node/executor and bounded timeout.
src/ros2_medkit_gateway/src/http/rest_server.cpp	Wires Ros2LifecycleStateReader into LifecycleHandlers at server construction.
src/ros2_medkit_gateway/include/ros2_medkit_gateway/core/http/handlers/lifecycle_handlers.hpp	Extends LifecycleHandlers constructor to accept an optional lifecycle reader (defaulted).
src/ros2_medkit_gateway/src/http/handlers/lifecycle_handlers.cpp	Updates default status logic for apps/components (lifecycle-aware apps; local components always ready).
src/ros2_medkit_gateway/test/test_lifecycle_status_helpers.cpp	Adds unit coverage for the helper mapping and lifecycle-service detection behavior.
src/ros2_medkit_gateway/test/test_ros2_lifecycle_state_reader.cpp	Adds unit coverage for Ros2LifecycleStateReader against an in-process GetState service.
src/ros2_medkit_gateway/test/test_lifecycle_handlers.cpp	Updates handler tests for new component semantics and adds stubbed-reader tests for lifecycle apps.
src/ros2_medkit_gateway/CMakeLists.txt	Adds new tests/targets and lifecycle_msgs dependency; registers lifecycle reader source in gateway_ros2.
src/ros2_medkit_gateway/package.xml	Adds lifecycle_msgs dependency required for GetState usage.
src/ros2_medkit_gateway/README.md	Updates user-facing docs for the new status derivation rules.
src/ros2_medkit_gateway/design/lifecycle.rst	Updates design doc to reflect lifecycle-based app status and new component readiness rule.