feat: add SQL editor, query results, and workspace panels

Add CodeMirror 6 SQL editor with Ctrl+Enter execution, ResultsTable
with virtual scrolling and resizable columns, ResultsPanel, EditableCell,
WorkspacePanel (editor + results split), and TabContent router.

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

src/components/editor/SqlEditor.tsx

@@ -0,0 +1,58 @@
+import CodeMirror from "@uiw/react-codemirror";
+import { sql, PostgreSQL } from "@codemirror/lang-sql";
+import { keymap } from "@codemirror/view";
+import { useCallback, useMemo } from "react";
+
+interface Props {
+  value: string;
+  onChange: (value: string) => void;
+  onExecute: () => void;
+}
+
+export function SqlEditor({ value, onChange, onExecute }: Props) {
+  const handleChange = useCallback(
+    (val: string) => {
+      onChange(val);
+    },
+    [onChange]
+  );
+
+  const extensions = useMemo(
+    () => [
+      sql({ dialect: PostgreSQL }),
+      keymap.of([
+        {
+          key: "Ctrl-Enter",
+          run: () => {
+            onExecute();
+            return true;
+          },
+        },
+        {
+          key: "Mod-Enter",
+          run: () => {
+            onExecute();
+            return true;
+          },
+        },
+      ]),
+    ],
+    [onExecute]
+  );
+
+  return (
+    <CodeMirror
+      value={value}
+      onChange={handleChange}
+      extensions={extensions}
+      theme="dark"
+      className="h-full text-sm"
+      basicSetup={{
+        lineNumbers: true,
+        foldGutter: true,
+        highlightActiveLine: true,
+        autocompletion: true,
+      }}
+    />
+  );
+}