feat: provider modules — ProviderProfile ABC, 30 providers, fetch_models, transport single-path

feat: provider modules — ProviderProfile ABC, 29 providers, fetch_models, transport single-path

Introduces providers/ as the single source of truth for every inference
provider. All 29 providers declared with correct data cross-checked against
auth.py, runtime_provider.py and auxiliary_client.py.

Rebased onto main (30307a980). Incorporates post-salvage fixes from
56724147e (gmi aux model google/gemini-3.1-flash-lite-preview, already set in providers/gmi.py).

providers/huggingface.py

@@ -0,0 +1,20 @@
+"""Hugging Face provider profile."""
+
+from providers import register_provider
+from providers.base import ProviderProfile
+
+huggingface = ProviderProfile(
+    name="huggingface",
+    aliases=("hf", "hugging-face", "huggingface-hub"),
+    env_vars=("HF_TOKEN",),
+    display_name="HuggingFace",
+    description="HuggingFace Inference API",
+    signup_url="https://huggingface.co/settings/tokens",
+    fallback_models=(
+        "Qwen/Qwen3.5-72B-Instruct",
+        "deepseek-ai/DeepSeek-V3.2",
+    ),
+    base_url="https://router.huggingface.co/v1",
+)
+
+register_provider(huggingface)