models: document Metis, the GreenPT decision model on /v1/systemone

Add a Decisions section: Metis returns probabilities/choices/scores rather than
text, is called at /v1/systemone with a member's normal gateway key, is
GreenPT-hosted (policy-based privacy, EU, renewable), and is metered
approximately (flat per-call estimate, not exact tokens).

models.md

@@ -197,6 +197,41 @@ numbers. Pricing here mirrors the `model_info` in the LiteLLM config
 (`code/litellm/config.yaml`), which is the authoritative source — the two are
 kept in sync.
 
+## Decisions
+
+Most models here generate text. **Metis**, from GreenPT, makes *decisions*
+instead: you give it a `state` (the situation, in plain text) plus up to 32
+typed questions, and it returns **probabilities, choices, and scores** — never
+prose. Use it when you want a calibrated judgement rather than a written
+answer: "should we…?", "which option…?", "how confident is that?".
+
+It's on the gateway at `/v1/systemone`, called with your normal co-op API key
+(the same key you use for chat):
+
+```bash
+curl https://gateway.inference.coop/v1/systemone \
+  -H "Authorization: Bearer ***" \
+  -H "Content-Type: application/json" \
+  -d '{
+    "model": "metis",
+    "state": "Your situation, described in plain text.",
+    "questions": {
+      "go":         {"type": "noul", "instructions": "Should we proceed?",
+                     "criteria": {"true": "proceed", "false": "do not proceed"}},
+      "which":      {"type": "choice", "instructions": "Which factor matters most?",
+                     "criteria": {"cost": "price", "speed": "latency"}},
+      "confidence": {"type": "score", "instructions": "How confident are you?",
+                     "criteria": ["very low", "low", "medium", "high", "very high"]}
+    }
+  }'
+```
+
+Metis is hosted by **GreenPT** — the same policy-based privacy, EU hosting, and
+100% renewable energy as the 🌱 chat models. Metering on this route is
+**approximate**: the gateway bills a small flat amount per call rather than the
+exact token count, so treat its spend figure as an estimate (it still counts
+toward your allowance).
+
 ## Limitations on privacy
 
 Only **Tinfoil** offers architectural privacy. The other providers are chosen