feat(phase-2.5): Task 6 cost_kind attribution + fees_eat_alpha threshold CLI

Task 6 del piano Phase 2.5 (deferito → ora completato):
- CostRecord: nuovo campo call_kind (default "hypothesis")
- CostTracker.record: accetta call_kind opzionale, summary include
  by_call_kind breakdown (hypothesis vs mutation)
- Schema cost_records: aggiunta colonna call_kind TEXT NOT NULL DEFAULT
  'hypothesis' + migration soft via ALTER TABLE in init_schema (silently
  catched per DB pre-Task 6)
- Repository.save_cost_record: nuova arg call_kind opzionale
- mutate_prompt_llm: accetta cost_tracker/repo/run_id opzionali e logga
  la call mutator con call_kind="mutation" quando sink presente
- weighted_random_mutate, next_generation: propagano cost sink
- orchestrator.run_phase1: passa cost_tracker+repo+run_id a
  next_generation solo se prompt_mutation_weight > 0

Esposto fees_eat_alpha_threshold come parametro AdversarialAgent
(default 0.5 = comportamento Phase 1.5 invariato), propagato via
RunConfig.fees_eat_alpha_threshold e flag CLI
--fees-eat-alpha-threshold. Abilita ablation con soglia 0.7-0.8 senza
modificare codice — adversarial finding dominante in tutti i run
Phase 2/2.5 (50+ HIGH per run).

Tests (+4 → 186 totale):
- test_cost_tracker: default call_kind="hypothesis"; breakdown
  by_call_kind con hypothesis+mutation
- test_mutation_prompt_llm: logging mutation cost con sink completo;
  backward compat senza sink (no errore)

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

scripts/run_phase1.py

@@ -37,6 +37,12 @@ def parse_args() -> argparse.Namespace:
         default=0.0,
         help="Phase 2.5: probabilità (0-1) che la mutazione invochi LLM mutator tier B",
     )
+    p.add_argument(
+        "--fees-eat-alpha-threshold",
+        type=float,
+        default=0.5,
+        help="Adversarial gate: kill se fees/gross_pnl > soglia (default 0.5, ablation 0.7)",
+    )
     return p.parse_args()
 
 
@@ -91,6 +97,7 @@ def main() -> None:
         n_trials_dsr=args.n_trials_dsr,
         db_path=settings.db_path,
         prompt_mutation_weight=args.prompt_mutation_weight,
+        fees_eat_alpha_threshold=args.fees_eat_alpha_threshold,
     )
 
     run_id = run_phase1(cfg, ohlcv=ohlcv, llm=llm)