feat: add database, role & privilege management

Add Admin sidebar tab with database/role management panels, role manager
workspace tab, and privilege dialogs. Backend provides 10 new Tauri
commands for CRUD on databases, roles, and privileges with read-only
mode enforcement. Context menus on schema tree nodes allow dropping
databases and viewing/granting table privileges.

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

src/components/management/CreateDatabaseDialog.tsx

@@ -0,0 +1,160 @@
+import { useState, useEffect } from "react";
+import {
+  Dialog,
+  DialogContent,
+  DialogHeader,
+  DialogTitle,
+  DialogFooter,
+} from "@/components/ui/dialog";
+import { Button } from "@/components/ui/button";
+import { Input } from "@/components/ui/input";
+import {
+  Select,
+  SelectContent,
+  SelectItem,
+  SelectTrigger,
+  SelectValue,
+} from "@/components/ui/select";
+import { useCreateDatabase, useRoles } from "@/hooks/use-management";
+import { toast } from "sonner";
+import { Loader2 } from "lucide-react";
+
+interface Props {
+  open: boolean;
+  onOpenChange: (open: boolean) => void;
+  connectionId: string;
+}
+
+export function CreateDatabaseDialog({ open, onOpenChange, connectionId }: Props) {
+  const [name, setName] = useState("");
+  const [owner, setOwner] = useState("__default__");
+  const [template, setTemplate] = useState("__default__");
+  const [encoding, setEncoding] = useState("UTF8");
+  const [connectionLimit, setConnectionLimit] = useState(-1);
+
+  const { data: roles } = useRoles(open ? connectionId : null);
+  const createMutation = useCreateDatabase();
+
+  useEffect(() => {
+    if (open) {
+      setName("");
+      setOwner("__default__");
+      setTemplate("__default__");
+      setEncoding("UTF8");
+      setConnectionLimit(-1);
+    }
+  }, [open]);
+
+  const handleCreate = () => {
+    if (!name.trim()) {
+      toast.error("Database name is required");
+      return;
+    }
+    createMutation.mutate(
+      {
+        connectionId,
+        params: {
+          name: name.trim(),
+          owner: owner === "__default__" ? undefined : owner,
+          template: template === "__default__" ? undefined : template,
+          encoding,
+          connection_limit: connectionLimit,
+        },
+      },
+      {
+        onSuccess: () => {
+          toast.success(`Database "${name}" created`);
+          onOpenChange(false);
+        },
+        onError: (err) => {
+          toast.error("Failed to create database", { description: String(err) });
+        },
+      }
+    );
+  };
+
+  return (
+    <Dialog open={open} onOpenChange={onOpenChange}>
+      <DialogContent className="sm:max-w-[480px]">
+        <DialogHeader>
+          <DialogTitle>Create Database</DialogTitle>
+        </DialogHeader>
+
+        <div className="grid gap-3 py-4">
+          <div className="grid grid-cols-4 items-center gap-3">
+            <label className="text-right text-sm text-muted-foreground">Name</label>
+            <Input
+              className="col-span-3"
+              value={name}
+              onChange={(e) => setName(e.target.value)}
+              placeholder="my_database"
+            />
+          </div>
+          <div className="grid grid-cols-4 items-center gap-3">
+            <label className="text-right text-sm text-muted-foreground">Owner</label>
+            <Select value={owner} onValueChange={setOwner}>
+              <SelectTrigger className="col-span-3">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value="__default__">Default</SelectItem>
+                {roles?.map((r) => (
+                  <SelectItem key={r.name} value={r.name}>
+                    {r.name}
+                  </SelectItem>
+                ))}
+              </SelectContent>
+            </Select>
+          </div>
+          <div className="grid grid-cols-4 items-center gap-3">
+            <label className="text-right text-sm text-muted-foreground">Template</label>
+            <Select value={template} onValueChange={setTemplate}>
+              <SelectTrigger className="col-span-3">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value="__default__">Default</SelectItem>
+                <SelectItem value="template0">template0</SelectItem>
+                <SelectItem value="template1">template1</SelectItem>
+              </SelectContent>
+            </Select>
+          </div>
+          <div className="grid grid-cols-4 items-center gap-3">
+            <label className="text-right text-sm text-muted-foreground">Encoding</label>
+            <Select value={encoding} onValueChange={setEncoding}>
+              <SelectTrigger className="col-span-3">
+                <SelectValue />
+              </SelectTrigger>
+              <SelectContent>
+                <SelectItem value="UTF8">UTF8</SelectItem>
+                <SelectItem value="LATIN1">LATIN1</SelectItem>
+                <SelectItem value="SQL_ASCII">SQL_ASCII</SelectItem>
+              </SelectContent>
+            </Select>
+          </div>
+          <div className="grid grid-cols-4 items-center gap-3">
+            <label className="text-right text-sm text-muted-foreground">Conn Limit</label>
+            <Input
+              className="col-span-3"
+              type="number"
+              value={connectionLimit}
+              onChange={(e) => setConnectionLimit(parseInt(e.target.value) || -1)}
+            />
+          </div>
+        </div>
+
+        <DialogFooter>
+          <Button variant="outline" onClick={() => onOpenChange(false)}>
+            Cancel
+          </Button>
+          <Button onClick={handleCreate} disabled={createMutation.isPending}>
+            {createMutation.isPending && (
+              <Loader2 className="mr-2 h-4 w-4 animate-spin" />
+            )}
+            Create
+          </Button>
+        </DialogFooter>
+      </DialogContent>
+    </Dialog>
+  );
+}