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/maze-ii.mdx

@@ -1,17 +1,17 @@
 ---
 title: "Activity: Maze II"
 date: "2021-06-05"
-categories: ["Activities", "All", "Simulator Activities"]
+categories: ["Activities", "Simulator Activities"]
 tags: ["Colour Sensors", "Branching", "Iteration", "Algorithm Design", "Ultrasonic", "IR", "Motors", "Intermediate"]
+codingSkills: ["Branching", "Iteration", "Algorithm Design"]
+roverConcepts: ["Colour", "Ultrasonic", "IR", "Motors"]
 excerpt: "Build on your maze solving skills by using both IR sensors and the ultrasonic sensor together to handle more complex maze layouts."
 featuredImage: "/images/resources/maze.png"
 ---
 
 Take your maze solving to the next level. In this intermediate challenge, you'll use both IR sensors alongside the ultrasonic sensor to make smarter decisions at intersections and handle more complex maze layouts.
 
-![](/images/content/1cf38b-maze.png)
-
-Activity Demonstration
+### Activity Demonstration
 
 ### Setup