docs: backfill env template and migration notes for M2

src/polygateway/embedding.py

@@ -158,7 +158,9 @@ class EmbeddingClient:
         outcomes = []
         for start in range(0, len(texts), self._batch_size):
             outcomes.append(
-                await self._embed_batch(texts[start : start + self._batch_size], session_id, parent_call_id)
+                await self._embed_batch(
+                    texts[start : start + self._batch_size], session_id, parent_call_id
+                )
             )
         return self._merge(outcomes)
 
@@ -394,9 +396,7 @@ class EmbeddingClient:
     def _total_cost(self, outcomes: list[_BatchOutcome]) -> float | None:
         if self._pricing is None:
             return None
-        costs = [
-            self._pricing.cost(o.source.model, o.result.prompt_tokens, 0) for o in outcomes
-        ]
+        costs = [self._pricing.cost(o.source.model, o.result.prompt_tokens, 0) for o in outcomes]
         known = [c for c in costs if c is not None]
         return sum(known) if known else None