fix(inbounds): preserve client data on delete and show traffic in detail

Deleting an inbound now only detaches its clients (removes the
client_inbounds rows). It no longer deletes client_traffics or client IP
logs: those are keyed centrally by email (one row per client) and must
survive, since a client may stay attached to other inbounds and is
managed from the Clients page.

Separately, /get/:id now uses a new GetInboundDetail that preloads and
enriches ClientStats, so hydrated records (info / QR / export) carry
per-client traffic instead of null. DBInbound.toJSON drops the internal
_clientStatsMap cache so it no longer leaks into the exported JSON.

frontend/src/models/dbinbound.ts

@@ -190,6 +190,12 @@ export class DBInbound {
         this._clientStatsMap = null;
     }
 
+    toJSON(): Record<string, unknown> {
+        const out: Record<string, unknown> = { ...(this as unknown as Record<string, unknown>) };
+        delete out._clientStatsMap;
+        return out;
+    }
+
     getClientStats(email: string): ClientStats | undefined {
         if (!this._clientStatsMap) {
             this._clientStatsMap = new Map();