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>

tests/unit/test_llm_client.py

@@ -0,0 +1,53 @@
+from multi_swarm.genome.hypothesis import HypothesisAgentGenome, ModelTier
+from multi_swarm.llm.client import CompletionResult, LLMClient
+
+
+def make_genome(tier: ModelTier) -> HypothesisAgentGenome:
+    return HypothesisAgentGenome(
+        system_prompt="x",
+        feature_access=["close"],
+        temperature=0.9,
+        top_p=0.95,
+        model_tier=tier,
+        lookback_window=200,
+        cognitive_style="physicist",
+    )
+
+
+def test_completion_tier_c_uses_openrouter(mocker):
+    fake_openai = mocker.MagicMock()
+    fake_response = mocker.MagicMock()
+    fake_response.choices = [mocker.MagicMock(message=mocker.MagicMock(content="(strategy ...)"))]
+    fake_response.usage = mocker.MagicMock(prompt_tokens=100, completion_tokens=200)
+    fake_openai.chat.completions.create.return_value = fake_response
+
+    mocker.patch("multi_swarm.llm.client.OpenAI", return_value=fake_openai)
+
+    client = LLMClient(openrouter_api_key="or-x", anthropic_api_key=None)
+    g = make_genome(ModelTier.C)
+    out = client.complete(g, system="sys", user="usr")
+
+    assert isinstance(out, CompletionResult)
+    assert out.text == "(strategy ...)"
+    assert out.input_tokens == 100
+    assert out.output_tokens == 200
+    assert out.tier == ModelTier.C
+    fake_openai.chat.completions.create.assert_called_once()
+
+
+def test_completion_tier_b_uses_anthropic(mocker):
+    fake_anthropic = mocker.MagicMock()
+    fake_msg = mocker.MagicMock()
+    fake_msg.content = [mocker.MagicMock(text="(strategy ...)")]
+    fake_msg.usage = mocker.MagicMock(input_tokens=80, output_tokens=150)
+    fake_anthropic.messages.create.return_value = fake_msg
+    mocker.patch("multi_swarm.llm.client.Anthropic", return_value=fake_anthropic)
+
+    client = LLMClient(openrouter_api_key="or-x", anthropic_api_key="an-x")
+    g = make_genome(ModelTier.B)
+    out = client.complete(g, system="sys", user="usr")
+
+    assert out.text == "(strategy ...)"
+    assert out.input_tokens == 80
+    assert out.output_tokens == 150
+    assert out.tier == ModelTier.B