feat: server-side launch preflight with structured checks and runtime AI wallet health

- POST /api/launch/preflight and GET /api/traders/:id/preflight run every
  launch prerequisite (AI model credential, claw402 wallet key + Base USDC
  balance, strategy, exchange config, live account state, funding minimums)
  and return a structured checklist with stable codes; minimums (1 USDC AI
  fee / 12 USDC trading) now live server-side and are exposed in the response.
- POST /traders/:id/start enforces the preflight (400 with error_key
  trader.start.preflight_failed + full checklist; ?force=true to override).
  Funding gates use max(available, equity) so restarting a bot with deployed
  margin is not blocked; indeterminate probes (RPC outage) degrade to
  warnings instead of blocking.
- Run loop now surfaces runtime health via GetStatus: safe_mode(+reason) and
  ai_wallet_status/balance (ok|low|empty|unknown), including typed detection
  of claw402 ErrInsufficientFunds instead of burying it in logs; safe-mode
  state is mutex-guarded for API readers.
- Onboarding wallet endpoints switch to the cached, error-aware balance query
  and report balance_status so the UI can tell an RPC outage from an empty
  wallet.

trader/auto_trader_decision.go

@@ -91,6 +91,19 @@ func (at *AutoTrader) GetStatus() map[string]interface{} {
 		}
 	}
 
+	// Runtime health: safe mode + AI fee wallet, so the dashboard can show a
+	// persistent banner instead of the user digging through logs.
+	safeMode, safeModeReason := at.safeModeState()
+	result["safe_mode"] = safeMode
+	if safeModeReason != "" {
+		result["safe_mode_reason"] = safeModeReason
+	}
+	if status, balance, checkedAt := at.aiWalletHealth(); status != "" {
+		result["ai_wallet_status"] = status
+		result["ai_wallet_balance_usdc"] = balance
+		result["ai_wallet_checked_at"] = checkedAt.Format(time.RFC3339)
+	}
+
 	return result
 }