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>

README.md

@@ -112,7 +112,7 @@ OPENROUTER_BASE_URL=https://openrouter.ai/api/v1
 LLM_MODEL_TIER_S=anthropic/claude-opus-4-7
 LLM_MODEL_TIER_A=anthropic/claude-sonnet-4-6
 LLM_MODEL_TIER_B=anthropic/claude-sonnet-4-6
-LLM_MODEL_TIER_C=qwen/qwen-2.5-72b-instruct
+LLM_MODEL_TIER_C=qwen/qwen3-235b-a22b-2507
 LLM_MODEL_TIER_D=meta-llama/llama-3.3-70b-instruct
 ```