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>

scripts/run_phase1.py

@@ -44,10 +44,6 @@ def main() -> None:
 
     llm = LLMClient(
         openrouter_api_key=settings.openrouter_api_key.get_secret_value(),
-        anthropic_api_key=(
-            settings.anthropic_api_key.get_secret_value()
-            if settings.anthropic_api_key else None
-        ),
         model_tier_s=settings.llm_model_tier_s,
         model_tier_a=settings.llm_model_tier_a,
         model_tier_b=settings.llm_model_tier_b,