Update README with LeetCode Daily Challenge

Author: jeremymanning

README.md

@@ -384,6 +384,7 @@ _**Note:** Our group is currently taking a break from grinding leetcode. The tab
 | July 6, 2025 | [1865](https://leetcode.com/problems/finding-pairs-with-a-certain-sum/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1865) | 🟡 Medium |
 | July 7, 2025 | [1353](https://leetcode.com/problems/maximum-number-of-events-that-can-be-attended/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1353) | 🟡 Medium |
 | July 8, 2025 | [1751](https://leetcode.com/problems/maximum-number-of-events-that-can-be-attended-ii/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1751) | 🔴 Hard |
+| July 9, 2025 | [3439](https://leetcode.com/problems/reschedule-meetings-for-maximum-free-time-i/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/3439) | 🟡 Medium |
 
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