Site audit: fix broken images, add activity metadata, clean up content

- Remove broken image references from 25 MDX files (deleted spacer/content images)
- Add codingSkills and roverConcepts frontmatter to 24 activity pages
- Fix "Activity Demonstration" headings in 15 activity files (plain text -> h3)
- Remove unused "All" category from 89 MDX files
- Decode HTML entities (> <  ) in 9 content files
- Escape bare < > characters in MDX to fix build errors
- Standardize contact email to contact@micromelon.com.au
- Add missing description to rover-repair-request metadata
- Include previous session work: about-us updates, difficulty filtering,
  LearningPathway component, expanded schools list, new product/resource images

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

content/resources/activity-ping-pong-shooter.mdx

@@ -1,8 +1,10 @@
 ---
 title: "Activity: Ping-Pong Shooter"
 date: "2023-10-12"
-categories: ["Activities", "All", "Simulator Activities"]
+categories: ["Activities", "Simulator Activities"]
 tags: ["Colour Sensors", "Branching", "Iteration", "Algorithm Design", "Advanced"]
+codingSkills: ["Branching", "Iteration", "Algorithm Design"]
+roverConcepts: ["Colour"]
 excerpt: "Use the ping-pong shooter attachment to locate and topple towers from a distance. The ultrasonic sensor can be used to find the tower by searching in a radar motion. Once the tower is located, the distance can be used to move the rover"
 featuredImage: "/images/resources/activity-ping-pong-shooter.jpg"
 ---
@@ -60,8 +62,6 @@ The rover will stop the motors and call the ‘*shoot*’ function to hit the to
 
 #### Complete Code:
 
-![](/images/content/0b24cc-code.png)
-
-**Tip:** 
+**Tip:**
 
 Our code aims to get as close as possible to the line and fire. However, another technique is to find the perfect distance from the tower to shoot from and use the ultrasonic to stop the robot.