feat: add cross-database entity lookup for searching column values across all databases

Enables searching for a specific column value (e.g. carrier_id=123) across all databases on a PostgreSQL server. The backend creates temporary connection pools per database (semaphore-limited to 5), queries information_schema for matching columns, and executes read-only SELECTs with real-time progress events. Results are grouped by database/table in a new "Entity Lookup" tab.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/layout/Toolbar.tsx

@@ -8,7 +8,7 @@ import { ReadOnlyToggle } from "@/components/layout/ReadOnlyToggle";
 import { useAppStore } from "@/stores/app-store";
 import { useConnections, useReconnect } from "@/hooks/use-connections";
 import { toast } from "sonner";
-import { Database, Plus, RefreshCw } from "lucide-react";
+import { Database, Plus, RefreshCw, Search } from "lucide-react";
 import type { ConnectionConfig, Tab } from "@/types";
 import { getEnvironment } from "@/lib/environment";
 
@@ -16,7 +16,7 @@ export function Toolbar() {
   const [listOpen, setListOpen] = useState(false);
   const [dialogOpen, setDialogOpen] = useState(false);
   const [editingConn, setEditingConn] = useState<ConnectionConfig | null>(null);
-  const { activeConnectionId, addTab } = useAppStore();
+  const { activeConnectionId, currentDatabase, addTab } = useAppStore();
   const { data: connections } = useConnections();
   const reconnectMutation = useReconnect();
   const activeConn = connections?.find((c) => c.id === activeConnectionId);
@@ -38,11 +38,24 @@ export function Toolbar() {
       type: "query",
       title: "New Query",
       connectionId: activeConnectionId,
+      database: currentDatabase ?? undefined,
       sql: "",
     };
     addTab(tab);
   };
 
+  const handleNewLookup = () => {
+    if (!activeConnectionId) return;
+    const tab: Tab = {
+      id: crypto.randomUUID(),
+      type: "lookup",
+      title: "Entity Lookup",
+      connectionId: activeConnectionId,
+      database: currentDatabase ?? undefined,
+    };
+    addTab(tab);
+  };
+
   return (
     <>
       <div
@@ -91,6 +104,17 @@ export function Toolbar() {
           New Query
         </Button>
 
+        <Button
+          variant="ghost"
+          size="sm"
+          className="h-7 gap-1.5"
+          onClick={handleNewLookup}
+          disabled={!activeConnectionId}
+        >
+          <Search className="h-3.5 w-3.5" />
+          Entity Lookup
+        </Button>
+
         <div className="flex-1" />
 
         <span className="text-xs font-semibold text-muted-foreground tracking-wide">