Module hierarchy 

Purpose: Expose task-hierarchy indexing, cycle detection, and tree rendering through a thin facade.

Responsibilities:

• Re-export the crate-visible queue::hierarchy API from focused companion modules.
• Keep indexing, cycle analysis, and rendering concerns split without changing caller imports.
• Preserve deterministic active/done hierarchy behavior across queue consumers.

Scope:

• Facade-only module wiring for hierarchy helpers used by queue validation and CLI flows.

Usage:

• Imported via crate::queue::hierarchy by CLI, validation, and task-decomposition helpers.

Invariants/Assumptions:

• Task IDs are unique across active + done files.
• Ordering remains deterministic: active tasks first, then done tasks.
• Cycle detection and rendering semantics stay behavior-compatible with the pre-split module.