Update MathAI 2026 conference deadlines

Updated the deadlines for MathAI 2026 based on the official conference website:
- Abstract submission: Feb 1 -> Feb 17, 2026
- Paper submission: Feb 19 -> Mar 1, 2026
- Decision notification: Mar 10 -> Mar 12, 2026

All deadlines verified from https://mathai.club

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/data/conferences/mathai.yml

@@ -36,15 +36,15 @@
   deadlines:
     - type: abstract
       label: Abstract submission deadline
-      date: '2026-02-01 23:59:59'
+      date: '2026-02-17 23:59:59'
       timezone: Europe/London
     - type: paper
       label: Full paper submission deadline
-      date: '2026-02-19 23:59:59'
+      date: '2026-03-01 23:59:59'
       timezone: Europe/London
     - type: notification
       label: Decision notification
-      date: '2026-03-10 23:59:59'
+      date: '2026-03-12 23:59:59'
       timezone: AoE
   city: Sochi
   country: Russia