feat(llm): make tier-C/tier-B model + OpenRouter URL configurable from .env

LLM_MODEL_TIER_C, LLM_MODEL_TIER_B e OPENROUTER_BASE_URL ora override-abili
via env. Default invariati (back-compat). LLMClient accetta i tre valori
come kwargs opzionali; run_phase1 li propaga da Settings.

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

tests/unit/test_config.py

@@ -40,3 +40,31 @@ def test_settings_requires_tokens(monkeypatch: pytest.MonkeyPatch) -> None:
         # Disable .env loading to keep the test deterministic regardless of
         # whether a developer's local .env exists and is populated.
         Settings(_env_file=None)  # type: ignore[call-arg]
+
+
+def test_settings_loads_llm_model_overrides(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("CERBERO_TESTNET_TOKEN", "tok-test")
+    monkeypatch.setenv("OPENROUTER_API_KEY", "or-key")
+    monkeypatch.setenv("LLM_MODEL_TIER_C", "deepseek/deepseek-chat")
+    monkeypatch.setenv("LLM_MODEL_TIER_B", "claude-opus-4-7")
+    monkeypatch.setenv("OPENROUTER_BASE_URL", "https://example.com/api/v1")
+
+    s = Settings(_env_file=None)  # type: ignore[call-arg]
+
+    assert s.llm_model_tier_c == "deepseek/deepseek-chat"
+    assert s.llm_model_tier_b == "claude-opus-4-7"
+    assert s.openrouter_base_url == "https://example.com/api/v1"
+
+
+def test_settings_llm_model_defaults(monkeypatch: pytest.MonkeyPatch) -> None:
+    monkeypatch.setenv("CERBERO_TESTNET_TOKEN", "tok-test")
+    monkeypatch.setenv("OPENROUTER_API_KEY", "or-key")
+    monkeypatch.delenv("LLM_MODEL_TIER_C", raising=False)
+    monkeypatch.delenv("LLM_MODEL_TIER_B", raising=False)
+    monkeypatch.delenv("OPENROUTER_BASE_URL", raising=False)
+
+    s = Settings(_env_file=None)  # type: ignore[call-arg]
+
+    assert s.llm_model_tier_c == "qwen/qwen-2.5-72b-instruct"
+    assert s.llm_model_tier_b == "claude-sonnet-4-6"
+    assert s.openrouter_base_url == "https://openrouter.ai/api/v1"