refactor: remove unused drizzle-orm import from markdown-viewer

Remove unused 'is' import from drizzle-orm in markdown-viewer.tsx (line 5).
This import was never used in the file and unnecessarily dragged ORM code
into the UI component's bundle chunk.

Benefits:
- Removes drizzle-orm from markdown-viewer bundle chunk
- Reduces bundle size for components using MarkdownViewer
- Cleaner imports with no unused dependencies
- Markdown viewer functionality unchanged

Fixes #1144

surfsense_web/components/markdown-viewer.tsx

@@ -2,7 +2,6 @@ import { createCodePlugin } from "@streamdown/code";
 import { createMathPlugin } from "@streamdown/math";
 import { Streamdown, type StreamdownProps } from "streamdown";
 import "katex/dist/katex.min.css";
-import { is } from "drizzle-orm";
 import Image from "next/image";
 import { cn } from "@/lib/utils";