feat: refresh UI with new typography and edit diff display (#63)

- Switch from Geist to Plus Jakarta Sans (body) and JetBrains Mono (code)
- Add visual diff display for edit_diagram tool showing search/replace pairs
- Update color palette to clean modern OKLCH-based scheme
- Improve chat message display with better styling and animations
- Add syntax-highlighted code blocks for XML/JSON output
- Improve scrollbar and shadow utilities

components/code-block.tsx

@@ -0,0 +1,39 @@
+"use client";
+
+import { Highlight, themes } from "prism-react-renderer";
+
+interface CodeBlockProps {
+    code: string;
+    language?: "xml" | "json";
+}
+
+export function CodeBlock({ code, language = "xml" }: CodeBlockProps) {
+    return (
+        <div className="overflow-hidden w-full">
+            <Highlight theme={themes.github} code={code} language={language}>
+                {({ className, style, tokens, getLineProps, getTokenProps }) => (
+                    <pre
+                        className="text-[11px] leading-relaxed overflow-x-auto overflow-y-auto max-h-48 scrollbar-thin break-all"
+                        style={{
+                            ...style,
+                            fontFamily: "var(--font-mono), ui-monospace, monospace",
+                            backgroundColor: "transparent",
+                            margin: 0,
+                            padding: 0,
+                            wordBreak: "break-all",
+                            whiteSpace: "pre-wrap",
+                        }}
+                    >
+                        {tokens.map((line, i) => (
+                            <div key={i} {...getLineProps({ line })} style={{ wordBreak: "break-all" }}>
+                                {line.map((token, key) => (
+                                    <span key={key} {...getTokenProps({ token })} />
+                                ))}
+                            </div>
+                        ))}
+                    </pre>
+                )}
+            </Highlight>
+        </div>
+    );
+}