fix(inbounds): forwarding echo lost in DBInbound — add the missing field

The edit modal seeds from the list row wrapped in DBInbound, whose
cloneProps only copies keys the instance already owns. DBInbound had
no forwarding field, so the stored ForwardingSpec JSON was silently
dropped on every row wrap and rawInboundToFormValues fell back to
direct — saved forwarding compiled and worked, but never echoed back
into the form. Backend/API carried the field correctly all along.

Regression test covers managed/manual/direct through the exact
row -> DBInbound -> form-values chain.

frontend/src/models/dbinbound.ts

@@ -39,6 +39,7 @@ export type DBInboundInit = Partial<{
   streamSettings: RawJsonField;
   tag: string;
   sniffing: RawJsonField;
+  forwarding: string;
   clientStats: ClientStats[];
   nodeId: number | null;
   shareAddrStrategy: string;
@@ -88,6 +89,7 @@ export class DBInbound {
   streamSettings: RawJsonField;
   tag: string;
   sniffing: RawJsonField;
+  forwarding: string;
   clientStats: ClientStats[];
   nodeId: number | null;
   shareAddrStrategy: string;
@@ -119,6 +121,7 @@ export class DBInbound {
     this.streamSettings = '';
     this.tag = '';
     this.sniffing = '';
+    this.forwarding = '';
     this.clientStats = [];
     this.nodeId = null;
     this.shareAddrStrategy = 'node';