Update README with LeetCode Daily Challenge

Author: jeremymanning

README.md

@@ -488,6 +488,7 @@ _**Note:** Our group is currently taking a break from grinding leetcode. The tab
 | October 18, 2025 | [3397](https://leetcode.com/problems/maximum-number-of-distinct-elements-after-operations/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/3397) | 🟡 Medium |
 | October 19, 2025 | [1625](https://leetcode.com/problems/lexicographically-smallest-string-after-applying-operations/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/1625) | 🟡 Medium |
 | October 20, 2025 | [2011](https://leetcode.com/problems/final-value-of-variable-after-performing-operations/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/2011) | 🟢 Easy |
+| October 21, 2025 | [3346](https://leetcode.com/problems/maximum-frequency-of-an-element-after-performing-operations-i/description/?envType=daily-question) | [Click here](https://github.com/ContextLab/leetcode-solutions/tree/main/problems/3346) | 🟡 Medium |
 
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