fix: parse MCP result payloads and drop place idempotency_key

Typed result structs replace empty envelopes. Equity place sends
ref_id only so live additionalProperties:false schemas accept the call.

accounts/accounts.go

@@ -60,8 +60,20 @@ type RealizedPnLRequest struct {
 	Timezone        string
 }
 
+// PnLBucket is one span bucket from get_realized_pnl.
+type PnLBucket struct {
+	Label   string
+	Amount  decimal.Decimal
+	Percent decimal.Decimal
+	Trades  int
+}
+
 // RealizedPnLResult is the parsed get_realized_pnl payload.
-type RealizedPnLResult struct{}
+type RealizedPnLResult struct {
+	Total   decimal.Decimal
+	Percent decimal.Decimal
+	Buckets []PnLBucket
+}
 
 // PnLTradeHistoryRequest is the argument set for get_pnl_trade_history.
 type PnLTradeHistoryRequest struct {
@@ -71,8 +83,20 @@ type PnLTradeHistoryRequest struct {
 	Cursor        string
 }
 
+// PnLTrade is one realizing trade from get_pnl_trade_history.
+type PnLTrade struct {
+	Symbol   string
+	Side     string
+	Quantity decimal.Decimal
+	Price    decimal.Decimal
+	PnL      decimal.Decimal
+}
+
 // PnLTradeHistoryResult is the parsed get_pnl_trade_history payload.
-type PnLTradeHistoryResult struct{}
+type PnLTradeHistoryResult struct {
+	Trades     []PnLTrade
+	NextCursor string
+}
 
 // AccountNumberRequest is a single account_number argument.
 type AccountNumberRequest struct {
@@ -80,10 +104,17 @@ type AccountNumberRequest struct {
 }
 
 // UpgradeInfoResult is the parsed upgrade-info payload.
-type UpgradeInfoResult struct{}
+type UpgradeInfoResult struct {
+	URL       string
+	WebURL    string
+	MobileURL string
+}
 
 // OnboardingInfoResult is the parsed crypto onboarding payload.
-type OnboardingInfoResult struct{}
+type OnboardingInfoResult struct {
+	URL    string
+	WebURL string
+}
 
 // SearchRequest is the argument set for search.
 type SearchRequest struct {
@@ -92,8 +123,18 @@ type SearchRequest struct {
 	Limit     int
 }
 
+// SearchHit is one instrument/pair/index from search.
+type SearchHit struct {
+	Symbol       string
+	Name         string
+	ID           string
+	InstrumentID string
+}
+
 // SearchResult is the parsed search payload.
-type SearchResult struct{}
+type SearchResult struct {
+	Results []SearchHit
+}
 
 // Accounts calls get_accounts and returns every account (no IRA/margin filter).
 func (c *Client) Accounts(ctx context.Context, req AccountsRequest) (AccountsResult, error) {