fix: add eslint-disable comments for set-state-in-effect rule in playground

The new react-hooks/set-state-in-effect ESLint rule flags setState calls
in useEffect hooks. These patterns are intentional in these components:
- ChatHeader: setMounted for hydration safety
- MessageBubble: setPartTimings for streaming state tracking
- SettingsSidebar: setEnvVars for localStorage initialization

🤖 Generated with [Claude Code](https://claude.ai/code)

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

apps/playground/src/components/chat/ChatHeader.tsx

@@ -1,8 +1,8 @@
 'use client';
 
 import { Button } from '@tpmjs/ui/Button/Button';
-import { useTheme } from 'next-themes';
 import Link from 'next/link';
+import { useTheme } from 'next-themes';
 import { useEffect, useState } from 'react';
 
 interface ChatHeaderProps {
@@ -13,8 +13,9 @@ export function ChatHeader({ onClear }: ChatHeaderProps): React.ReactElement {
   const { theme, setTheme } = useTheme();
   const [mounted, setMounted] = useState(false);
 
-  // Avoid hydration mismatch
+  // Avoid hydration mismatch - this is intentional for SSR
   useEffect(() => {
+    // eslint-disable-next-line react-hooks/set-state-in-effect
     setMounted(true);
   }, []);
 

apps/playground/src/components/chat/MessageBubble.tsx

@@ -53,6 +53,7 @@ export function MessageBubble({
 
     const now = Date.now();
 
+    // eslint-disable-next-line react-hooks/set-state-in-effect
     setPartTimings((prev) => {
       const updated = new Map(prev);
 

apps/playground/src/components/sidebar/SettingsSidebar.tsx

@@ -22,6 +22,7 @@ export function SettingsSidebar(): React.ReactElement {
     try {
       const stored = localStorage.getItem(ENV_STORAGE_KEY);
       if (stored) {
+        // eslint-disable-next-line react-hooks/set-state-in-effect
         setEnvVars(JSON.parse(stored));
       }
     } catch (error) {