feat(llm): unified client for OpenRouter (Qwen) + Anthropic (Sonnet)

LLMClient instrada richieste in base a ModelTier del genome:
- Tier C -> Qwen 2.5 72B via OpenRouter (chat completions)
- Tier B -> Sonnet 4.6 via Anthropic (messages API)
CompletionResult dataclass frozen con text, tokens, tier, model.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/multi_swarm/llm/client.py

@@ -0,0 +1,80 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+from anthropic import Anthropic
+from openai import OpenAI
+
+from ..genome.hypothesis import HypothesisAgentGenome, ModelTier
+
+# Modelli configurati per Phase 1
+MODEL_TIER_C = "qwen/qwen-2.5-72b-instruct"  # via OpenRouter
+MODEL_TIER_B = "claude-sonnet-4-6"  # via Anthropic
+OPENROUTER_BASE_URL = "https://openrouter.ai/api/v1"
+
+
+@dataclass(frozen=True)
+class CompletionResult:
+    text: str
+    input_tokens: int
+    output_tokens: int
+    tier: ModelTier
+    model: str
+
+
+class LLMClient:
+    def __init__(
+        self,
+        openrouter_api_key: str,
+        anthropic_api_key: str | None = None,
+    ) -> None:
+        self._openrouter = OpenAI(api_key=openrouter_api_key, base_url=OPENROUTER_BASE_URL)
+        self._anthropic = Anthropic(api_key=anthropic_api_key) if anthropic_api_key else None
+
+    def complete(
+        self,
+        genome: HypothesisAgentGenome,
+        system: str,
+        user: str,
+        max_tokens: int = 2000,
+    ) -> CompletionResult:
+        if genome.model_tier == ModelTier.C:
+            resp = self._openrouter.chat.completions.create(
+                model=MODEL_TIER_C,
+                messages=[
+                    {"role": "system", "content": system},
+                    {"role": "user", "content": user},
+                ],
+                temperature=genome.temperature,
+                top_p=genome.top_p,
+                max_tokens=max_tokens,
+            )
+            usage = resp.usage
+            assert usage is not None
+            return CompletionResult(
+                text=resp.choices[0].message.content or "",
+                input_tokens=usage.prompt_tokens,
+                output_tokens=usage.completion_tokens,
+                tier=ModelTier.C,
+                model=MODEL_TIER_C,
+            )
+
+        if self._anthropic is None:
+            raise RuntimeError("ANTHROPIC_API_KEY required for tier B genomes")
+
+        msg = self._anthropic.messages.create(
+            model=MODEL_TIER_B,
+            system=system,
+            messages=[{"role": "user", "content": user}],
+            temperature=genome.temperature,
+            top_p=genome.top_p,
+            max_tokens=max_tokens,
+        )
+        text = "".join(block.text for block in msg.content if hasattr(block, "text"))
+        return CompletionResult(
+            text=text,
+            input_tokens=msg.usage.input_tokens,
+            output_tokens=msg.usage.output_tokens,
+            tier=ModelTier.B,
+            model=MODEL_TIER_B,
+        )