Adds is_civitai_available() and civitai_fetch_by_hash() with SILENT
fallback (returns None) when companion missing. No RuntimeError because
CivitAI lookup is an optional convenience — the LoRA workflow works
without auto-trigger detection.
Pre-existing callers already handle None on network failure, so this
facade is drop-in compatible.
Also updates tests/conftest.py to importlib-load the real civitai.py
(matches Phase 1/2 patterns for remote_vae + distribution).
Callers (config_builder_node.py + lora_utils.py) still import from
.network_utils as of this commit; the swap lands in the next commit.
Jason Hoku
23c857353b