feat(config): align tier defaults to cost-conscious models + qwen3-235b on tier C

- Tier S → google/gemini-3-flash-preview ($0.50/$3.00)
- Tier A/B → deepseek/deepseek-v4-flash ($0.14/$0.28)
- Tier C → qwen/qwen3-235b-a22b-2507 ($0.071/$0.10) — Phase 2 target
- Tier D → openai/gpt-oss-20b ($0.03/$0.14)

Aggiornato cost_tracker con prezzi reali per tier. Defaults config.py
ora rispecchiano .env corrente per evitare divergenze dead-code.

Tier S/A/B/D restano cablati ma non ancora invocati nel loop Phase 2
(solo Hypothesis tier C attivo).

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

src/multi_swarm/config.py

@@ -25,11 +25,11 @@ class Settings(BaseSettings):
 
     openrouter_api_key: SecretStr
 
-    llm_model_tier_s: str = "anthropic/claude-opus-4-7"
-    llm_model_tier_a: str = "anthropic/claude-sonnet-4-6"
-    llm_model_tier_b: str = "anthropic/claude-sonnet-4-6"
-    llm_model_tier_c: str = "qwen/qwen-2.5-72b-instruct"
-    llm_model_tier_d: str = "meta-llama/llama-3.3-70b-instruct"
+    llm_model_tier_s: str = "google/gemini-3-flash-preview"
+    llm_model_tier_a: str = "deepseek/deepseek-v4-flash"
+    llm_model_tier_b: str = "deepseek/deepseek-v4-flash"
+    llm_model_tier_c: str = "qwen/qwen3-235b-a22b-2507"
+    llm_model_tier_d: str = "openai/gpt-oss-20b"
     openrouter_base_url: str = "https://openrouter.ai/api/v1"
 
     run_name: str = "phase1-spike-001"