Split the structures layer into FlashRT-Structures; keep the catalog as flash_rt.catalog

[LiangSu8899]

What moves out

The host-attach layer — discovery, calibration collection, schemes, gates, guard/swap, the doors, every executable form, the transformers / diffusers / vLLM / SGLang adapters, the explicit pipeline examples, the structures docs and AGENTS.md — now lives in FlashRT-Structures as the flashrt-structures distribution, importable as flashrt_structures. Extracted with history.

It never had a consumer inside this package (no import from flash_rt.api, models, frontends, runtime, serving), and its kernels arrive from the kernel hub rather than from csrc/, so it was a second product sharing this package's name and wheel.

What stays

• flash_rt.catalog — the contract data every host reads: structure specs with their plain-torch references (flash_rt/catalog/structures/), per-host bindings (flash_rt/catalog/bindings/), and the two loaders. Consumed by the runtime exporters, the native host adapters, and the new package (through the pure-Python flash-rt wheel).
• flash_rt/runtime/provider.py — the captured-graph provider that packages a host's CUDA graph as frt_model_runtime_v1, beside the runtime it targets.
• flash_rt/core/parity.py — the cosine / max-abs / p99-abs judge, now the single definition shared by the NPU verifier and the new package's gates.
• The six catalog contract tests, renamed test_catalog_*.

flash_rt.structures raises an ImportError naming the new distribution. README, CONTRIBUTING and pyproject point at the new repository; the hub extra goes with the layer that used it. Version bumps to 0.2.0: the pure-Python wheel now ships flash_rt.catalog, which flashrt-structures requires.

Verification

• flash_rt.catalog: 17 structures, 27 bindings load; load_binding and reference resolution work.
• Retained tests: 66 passed (tests/test_catalog_*.py, tests/test_core_quantization.py).
• No remaining flash_rt.structures / flash_rt/structures references outside the shim.
• FlashRT-Structures against this branch: all modules import; CPU test set 248 passed, 10 skipped (the two *_gpu tests were not run).

Follow-up

#186 (native ggml adapter) is rebased onto this once it lands: its adapter already sits at hosts/ggml, and its catalog and binding additions move under flash_rt/catalog/.