Hardening round 2: healthcheck, audit anchor, return_4h, exec config, signals

Sei interventi MEDIA priorità sul sistema. 323 test pass, mypy strict
pulito, ruff clean.

1. Docker HEALTHCHECK + cerbero-bite healthcheck:
   - nuovo subcommand che esce 0 se kill_switch=0 e last_health_check
     entro --max-staleness-s (default 600s);
   - HEALTHCHECK direttiva nel Dockerfile (60s interval, 5s timeout,
     start_period 120s, retries 3);
   - healthcheck definition nel docker-compose.yml.

2. Audit hash chain anti-truncation:
   - migration 0002: nuova colonna system_state.last_audit_hash;
   - AuditLog accetta callback on_append, dependencies.py la wire al
     repository.set_last_audit_hash;
   - Orchestrator.boot verifica che il tail file matcha l'anchor
     persistito; mismatch → kill switch CRITICAL.

3. return_4h bootstrap da deribit get_historical:
   - quando dvol_history è vuoto _fetch_return_4h cade su
     deribit.historical_close (1h candle 4h fa);
   - alert LOW se anche il fallback fallisce.

4. execution.environment + execution.eur_to_usd in strategy.yaml:
   - ExecutionConfig promosso a typed schema con i due campi
     consumati al boot;
   - CLI start preferisce i valori da config; CLI flag overridano
     solo quando differenti dai default.

5. Cycle correlation ID:
   - structlog.contextvars.bind_contextvars in run_entry/run_monitor/
     run_health propaga cycle_id e cycle nei log strutturati.

6. SIGTERM/SIGINT clean shutdown:
   - run_forever installa loop.add_signal_handler per SIGTERM e
     SIGINT; il segnale set()ta un asyncio.Event che termina il
     blocco principale, scheduler.shutdown e ctx.aclose finalizzano.

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

src/cerbero_bite/runtime/dependencies.py

@@ -103,7 +103,23 @@ def build_runtime(
     finally:
         conn.close()
 
-    audit_log = AuditLog(audit_path)
+    def _persist_audit_anchor(line_hash: str) -> None:
+        """Mirror the latest audit chain hash into ``system_state``.
+
+        Best-effort: if SQLite is locked by another writer the audit
+        log itself is still consistent, the anchor will catch up on
+        the next append.
+        """
+        anchor_conn = connect(db_path)
+        try:
+            with transaction(anchor_conn):
+                repository.set_last_audit_hash(anchor_conn, hex_hash=line_hash)
+        except Exception:  # pragma: no cover — durability is best-effort
+            pass
+        finally:
+            anchor_conn.close()
+
+    audit_log = AuditLog(audit_path, on_append=_persist_audit_anchor)
     kill_switch = KillSwitch(
         connection_factory=lambda: connect(db_path),
         repository=repository,