Add schedule for April 7 kick-off meeting

Added schedule section with details for April 7 meeting.

Author: fcczzz

src/2026_spring.md

@@ -10,8 +10,10 @@
 
 The playback video and text summary will be uploaded to <a href="https://space.bilibili.com/3493280155175017/channel/collectiondetail?sid=3787828" target="_blank">bilibili</a> and <a href="https://www.zhihu.com/column/c_1819774258647277568" target="_blank">zhihu</a> as soon as possible.
 
+## Schedule
+### April 7
 
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-
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+- 💡 Kick-off meeting
+- 🙎‍♂️ Zewen Jin, Chizheng Fang, Yuzhe Li, Mulong Li and Shen Fu
+- [📕 slides]
+<br><br>