feat(protocol): define core ROS interfaces

[Staaaaaaaaar]

Motivation

Implements roadmap PR 02 — Core ROS Interfaces from
docs/architecture-and-development-plan.md.

Environment, Agent, and Experiment components need one implementation-independent
ROS 2 wire contract before their runtime behavior can be developed independently.

Scope

• Add the ament_cmake rh_interfaces package.
• Define four messages: ComponentStatus, EpisodeState, PointNavTask, and
  EpisodeResult.
• Define four services: ResetEnv, ResetAgent, StartEpisode, and
  AbortEpisode.
• Freeze lifecycle and termination-reason numeric values.
• Document topic/service ownership, units, frame semantics, idempotency keys,
  opaque text fields, and compatibility rules.
• Add cross-language interface contract tests under tests/contracts.
• Include top-level contract packages and Python tests in the standard
  make dev-check path.

Out of scope

• Publishers, subscribers, service servers/clients, or runtime nodes.
• QoS profiles, deadlines, heartbeat handling, reset deduplication, and sequence
  guards; these belong to PR 04.
• Core models, configuration validation, and state-machine behavior; these
  belong to PR 03 and later orchestration PRs.
• A shared error-code catalog, generic Observation message, or long-running
  Episode Action.
• Isaac Sim, Go2, Agent, Task, or Evaluator implementations.

Architecture changes

This follows the existing architecture baseline: rh_interfaces is a leaf ROS
interface package shared by all three runtime containers. It depends only on
ROS interface-generation/runtime packages plus builtin_interfaces and
geometry_msgs; it has no dependency on a RoboHarness implementation package.

The default generated states are deliberately non-operational:
ComponentStatus.STARTING=0 and EpisodeState.PREPARING=0. READY and RUNNING
therefore require explicit assignment. EpisodeState.NONE=0 represents the
absence of a committed termination reason.

Existing numeric values are stable wire values. Future values may be appended,
but existing values must not be reordered or reused.

Implementation

• Configure all eight interfaces with rosidl_generate_interfaces and export
  rosidl_default_runtime.
• Keep Episode lifecycle state orthogonal to its termination reason.
• Carry reset request_id values as opaque idempotency keys without embedding
  runtime deduplication policy in the message package.
• Keep EpisodeResult compact and refer to the durable JSON result through an
  opaque result_uri.
• Treat detail, abort reason, and result_uri as opaque strings that must
  never be parsed for control decisions.
• Use package version 0.0.0 and license value NOASSERTION until release and
  licensing metadata are finalized by roadmap PR 18.

Testing

Validated in the pinned Ubuntu 22.04 / ROS 2 Humble development container:

$ make dev-check
Summary: 2 packages finished
Summary: 4 tests, 0 errors, 0 failures, 0 skipped

Coverage includes:

• rosidl C/C++/Python generation;
• linked C++ message and service typesupport;
• Python serialization/deserialization round trips for every request, response,
  and message type;
• exact field names, order, and ROS types;
• stable lifecycle and termination numeric values;
• package dependency-boundary enforcement;
• CMake, XML, repository, Markdown/YAML, and Ruff checks.

The contract suite contains 3 C++ cases and 26 Python cases.

Acceptance criteria

• Scope and out-of-scope match the implementation.
• Build, lint, and relevant tests pass.
• Documentation is updated.
• Acceptance evidence is included.
• C++ and Python typesupport are generated and usable.
• The interface package has no implementation-package dependencies.
• Example messages and service payloads round-trip successfully.

Known limitations

• Interface classes do not validate identifiers, finite numeric values, frames,
  radii, or timeouts; PR 03 owns domain validation.
• Non-zero reset/status error codes remain component-specific until repeated
  implementation needs justify a shared catalog.
• QoS and runtime idempotency semantics are documented but not implemented in
  this interface-only PR.
• Project release version and license metadata are intentionally not finalized.

Follow-up

Roadmap PR 03 will add ROS-independent Experiment/Episode/PointNav models,
configuration loading, validation, and state-transition guards, with conversion
tests against these interfaces.