refactor(llm): route all tiers via OpenRouter, drop Anthropic SDK

Tutti i tier (S/A/B/C/D) ora passano per OpenRouter via OpenAI SDK.
Modelli Anthropic raggiungibili via prefisso `anthropic/...`.

- pyproject: rimosso `anthropic>=0.39` da deps + uv.lock
- config: rimosso `anthropic_api_key` field
- LLMClient: dispatch unico, single client OpenAI con base_url OpenRouter
- defaults S/A/B → `anthropic/claude-{opus-4-7,sonnet-4-6}`
- retry exceptions: solo openai.* (drop anthropic.*)
- test rinominati e adattati: tier S/A/B mockano OpenAI con prefisso `anthropic/`
- rimosso test `tier_S_without_anthropic_key_raises` (non più rilevante)

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

tests/unit/test_config.py

@@ -19,7 +19,6 @@ def test_settings_loads_from_env(monkeypatch: pytest.MonkeyPatch) -> None:
     monkeypatch.setenv("CERBERO_MAINNET_TOKEN", "tok-main")
     monkeypatch.setenv("CERBERO_BOT_TAG", "swarm-poc-phase1")
     monkeypatch.setenv("OPENROUTER_API_KEY", "or-key")
-    monkeypatch.setenv("ANTHROPIC_API_KEY", "an-key")
     monkeypatch.setenv("RUN_NAME", "test-run")
 
     s = Settings()  # type: ignore[call-arg]
@@ -74,9 +73,9 @@ def test_settings_llm_model_defaults(monkeypatch: pytest.MonkeyPatch) -> None:
 
     s = Settings(_env_file=None)  # type: ignore[call-arg]
 
-    assert s.llm_model_tier_s == "claude-opus-4-7"
-    assert s.llm_model_tier_a == "claude-sonnet-4-6"
-    assert s.llm_model_tier_b == "claude-sonnet-4-6"
+    assert s.llm_model_tier_s == "anthropic/claude-opus-4-7"
+    assert s.llm_model_tier_a == "anthropic/claude-sonnet-4-6"
+    assert s.llm_model_tier_b == "anthropic/claude-sonnet-4-6"
     assert s.llm_model_tier_c == "qwen/qwen-2.5-72b-instruct"
     assert s.llm_model_tier_d == "meta-llama/llama-3.3-70b-instruct"
     assert s.openrouter_base_url == "https://openrouter.ai/api/v1"