libero: drop orphaned tasks/ + stale manifest.json (old removed-pack format); assets/ + assets_manifest.json are canonical

libero: README + assets_manifest describe the canonical native pack (assets/ consumed by native_libero)

libero: add init_state to per-task goal.json (deterministic BDDL reset for registered tasks)

Add libero/: 130 base LIBERO tasks vendored as portable MJCF + 193 deduped shared assets (library-free; checker 130/130 bitwise)