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.mdx

@@ -1,17 +1,17 @@
 ---
 title: "Activity: Maze I"
 date: "2021-06-04"
-categories: ["Activities", "All", "Simulator Activities"]
+categories: ["Activities", "Simulator Activities"]
 tags: ["Colour Sensors", "Branching", "Iteration", "Algorithm Design", "Ultrasonic", "IR", "Motors", "Beginner"]
+codingSkills: ["Branching", "Iteration", "Algorithm Design"]
+roverConcepts: ["Ultrasonic", "IR", "Motors"]
 excerpt: "Learn the basics of maze solving using the ultrasonic and IR sensors to detect walls and navigate simple paths."
 featuredImage: "/images/resources/maze.png"
 ---
 
 Navigate your rover through a maze using the ultrasonic sensor to detect walls ahead and the IR sensor to check for walls to the side. This beginner approach introduces the fundamentals of maze solving with simple branching logic.
 
-![](/images/content/1cf38b-maze.png)
-
-Activity Demonstration
+### Activity Demonstration
 
 ### Setup