fix(hwfit): filter non-GGUF models on Windows (#2530)

Odysseus only supports llama.cpp on Windows (vLLM/SGLang are
explicitly blocked). llama.cpp requires GGUF, so AWQ/GPTQ/FP8
safetensors models without a GGUF alternate should not be
recommended in the Cookbook on Windows hosts.

Changes:
- hardware.py: add 'platform': 'windows' to _detect_windows()
  so downstream logic can identify Windows hosts.
- fit.py: include is_windows in the existing GGUF-only filter
  alongside apple_silicon and consumer_amd.
- tests: add test_hwfit_windows.py with regression tests.

Fixes #122, #614 (root cause: unservable models recommended).

tests/test_hwfit_windows.py

@@ -0,0 +1,74 @@
+"""Windows support for Cookbook hardware-fit.
+
+Odysseus only supports llama.cpp on Windows (vLLM/SGLang are explicitly
+blocked). llama.cpp requires GGUF, so non-GGUF models — including AWQ/GPTQ/
+FP8 safetensors repos — must be filtered out on Windows so the Cookbook does
+not recommend models the user cannot actually serve.
+"""
+
+from services.hwfit.fit import rank_models
+from services.hwfit.models import get_models
+
+
+def _windows_system(ram_gb=32.0, vram_gb=16.0):
+    return {
+        "has_gpu": True,
+        "backend": "cuda",
+        "gpu_name": "NVIDIA RTX 4060",
+        "gpu_vram_gb": vram_gb,
+        "gpu_count": 1,
+        "available_ram_gb": ram_gb * 0.7,
+        "total_ram_gb": ram_gb,
+        "platform": "windows",
+    }
+
+
+def _cuda_system():
+    return {
+        "has_gpu": True,
+        "backend": "cuda",
+        "gpu_name": "NVIDIA RTX 4090",
+        "gpu_vram_gb": 24.0,
+        "gpu_count": 1,
+        "available_ram_gb": 32.0,
+        "total_ram_gb": 64.0,
+    }
+
+
+def test_only_gguf_models_recommended_on_windows():
+    """llama.cpp (GGUF) is the only servable path on Windows, so every model
+    recommended there must ship a real GGUF — no vLLM-only AWQ/GPTQ/FP8."""
+    catalog = {m["name"]: m for m in get_models()}
+    unservable = [
+        r["name"] for r in rank_models(_windows_system(), limit=900)
+        if not (catalog.get(r["name"], {}).get("is_gguf")
+                or catalog.get(r["name"], {}).get("gguf_sources"))
+    ]
+    assert unservable == [], f"{len(unservable)} non-GGUF models on Windows, e.g. {unservable[:3]}"
+
+
+def test_safetensors_models_still_recommended_on_cuda():
+    """Regression guard: the GGUF-only rule must not leak onto CUDA."""
+    names = {r["name"] for r in rank_models(_cuda_system(), limit=900)}
+    assert "microsoft/Phi-mini-MoE-instruct" in names
+
+
+def test_awq_model_hidden_on_windows():
+    """The user's reported issue: Qwen2.5-3B-Instruct-AWQ is AWQ-only and must
+    not be recommended on Windows where it cannot be served."""
+    names = {r["name"] for r in rank_models(_windows_system(), limit=900)}
+    assert "Qwen/Qwen2.5-3B-Instruct-AWQ" not in names
+
+
+def test_awq_model_visible_on_cuda():
+    """The same AWQ model should still be visible on CUDA where vLLM can
+    serve it."""
+    names = {r["name"] for r in rank_models(_cuda_system(), limit=900)}
+    assert "Qwen/Qwen2.5-3B-Instruct-AWQ" in names
+
+
+def test_gguf_alternate_still_recommended_on_windows():
+    """Qwen2.5-3B-Instruct (the base model) has a GGUF source, so it should
+    still appear on Windows even though the AWQ variant is hidden."""
+    names = {r["name"] for r in rank_models(_windows_system(), limit=900)}
+    assert "Qwen/Qwen2.5-3B-Instruct" in names