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>

scripts/run_phase1.py

@@ -48,6 +48,9 @@ def main() -> None:
             settings.anthropic_api_key.get_secret_value()
             if settings.anthropic_api_key else None
         ),
+        model_tier_c=settings.llm_model_tier_c,
+        model_tier_b=settings.llm_model_tier_b,
+        openrouter_base_url=settings.openrouter_base_url,
     )
 
     cfg = RunConfig(