Add August 2026 announcement and Gridfinity challenge; update wiki current/upcoming challenges and important dates

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

announcements/August2026.md

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+# 3D Fuel August Meetup - Meeting Announcement
+
+## Email Subject Line
+
+Join Us in August: 3D Printing Meetup + Gridfinity Extravaganza!
+
+---
+
+## Email Body
+
+Hey everyone!
+
+Join us for the **August 3D Printing Meetup**.
+
+For more information about the meetup and community events, visit [www.fargo3d.com](https://www.fargo3d.com)
+
+**Time: 6:00 - 8:00 PM**
+**Location**: West Fargo Public Library, 215 Third St. E., West Fargo, ND 58078
+
+Come join us to catch the latest industry news updates from John and share your organizational wins!
+
+### August Challenge: Gridfinity Extravaganza
+
+This month's challenge is all about the **Gridfinity** system! Whether you're a pro at organizing or just starting out, we want to see your best modules.
+
+**Challenge Requirements:**
+- Bring a **Gridfinity Base**.
+- Bring **one top accessory** that fits into that base (this can be a bin, a cover, a tool holder, etc.).
+- Be ready to show how it works and why you chose that specific part!
+
+This is a great opportunity to see different variations of the Gridfinity system and pick up some new ideas for your own workshop.
+
+See you there!