P5A Execution Plan

Inspect workbench state ownership and compiler output writer; keep export sourced from the current compiled state, not host paths.
Add deterministic root-flat ZIP writer plus validation and CLI entry point.
Add Web download action using the same writer.
Add fixtures for root layout, content determinism, manifest/source parity and edited-state export.
Export both supported-area fixtures for P5B, run compiler tests, then publish a compiler release.

Rollback: remove the export entry point; no host behavior changes in this subtask.