ORCH-6: src/projects.py introduces ProjectConfig + resolvers
(get_project_by_plane_id/by_repo, known_plane_project_ids) keyed by
Plane project uuid. Source: ORCH_PROJECTS_JSON env (config.projects_json),
with a built-in default registry (enduro-trails + orchestrator) and
robust parsing (malformed JSON/entries fall back to default).
