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

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

challenges/August-2026/readme.md

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+---
+gitea: none
+tags:
+ - challenge
+ - challenge-009
+---
+[← Back to Home Page](Home)
+
+# Current Challenge: August 2026
+
+## Challenge: Gridfinity Extravaganza
+
+This month, we're diving into the world of **Gridfinity**! Whether you are a long-time user or completely new to the system, it's time to show off your organizational skills.
+
+### The Focus: Organizational Efficiency
+The goal is to create a functional and well-executed Gridfinity module that solves a real-world storage problem or simply looks great.
+
+### Submission Requirements
+
+* **Physical Model**: Bring your prints to the August meetup.
+* **Required Components**: 
+    * At least one **Gridfinity Base** (the base plate).
+    * One **Top Accessory** that fits into that base. This can be a bin, a cover, a tool holder, or any other accessory of your choice.
+* **The Story**: Be ready to explain what the accessory is for and how you approached the print.
+
+### Judging & Prize
+
+* **Voting**: The group will vote on their favorite entry based on utility, creativity, and print quality.
+* **Prize**: The winner will receive a **free spool of filament**!
+
+### Timeline
+
+* **Challenge Announcement**: July 2026 (at July 15th meetup)
+* **Show & Tell / Voting**: August 2026 (during August meetup)
+* **Winner Announcement**: August 2026 (end of August meetup)
+
+---
+
+**This challenge is active for August 2026**