feat(task): implement PointNav task module

[Staaaaaaaaar]

Motivation

Implement roadmap PR 08 so the single-Episode lifecycle carries concrete PointNav semantics without introducing a universal Task hierarchy.

Scope

• add the rh_pointnav ROS 2 package
• validate immutable 3D PointNav definitions and identity
• provide 3D distance, success-radius, and simulation-time timeout predicates
• publish one reliable transient-local PointNavTask snapshot
• integrate concrete Task publication through a generic rh_experiment factory boundary
• verify Env, Agent, and Evaluator receive the same snapshot before READY

Architecture Changes

rh_experiment owns only an in-process task-publisher protocol and remains independent of concrete Task packages. rh_pointnav supplies the publisher through a composed orchestrator entrypoint. This keeps future Task implementations separate while preserving one authoritative lifecycle.

The initial state remains a complete 3D pose. A PointNav goal is strictly a 3D position in map and has no yaw or orientation semantics.

Testing

• make dev-check
• 13 packages built
• 179 tests, 0 errors, 0 failures, 0 skipped
• verified ros2 pkg executables rh_pointnav exposes rh_pointnav orchestrator

Acceptance Criteria

• Env, Agent, and Evaluator receive the same task snapshot
• transient-local delivery works for late subscribers
• invalid frame, radius, timeout, identity, and non-finite values are rejected
• invalid PointNav input is rejected before reset/start coordination can produce motion
• task publication occurs after Env/Agent reset and before READY

Known Limitations

• no evaluator aggregation or trajectory observation
• no automatic goal sampling
• no PoseNav or other Task hierarchy

Follow-up

PR 09 will consume these typed predicates from the simple navigation evaluator.

Roadmap: PR 08 — PointNav Task Module