Update EMNLP 2025 System Demonstrations deadlines

- Added notification of acceptance deadline (September 9, 2025)
- Added camera-ready submission deadline (September 19, 2025)

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

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

src/data/conferences/emnlp_system_demonstrations_track.yml

@@ -9,6 +9,14 @@
       label: Paper submission deadline
       date: '2025-07-04 23:59:59'
       timezone: AoE
+    - type: notification
+      label: Notification of acceptance
+      date: '2025-09-09 23:59:59'
+      timezone: AoE
+    - type: camera_ready
+      label: Camera-ready submission
+      date: '2025-09-19 23:59:59'
+      timezone: AoE
   date: November 5-9, 2025
   tags:
   - natural-language-processing