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/robot-simulator.mdx

@@ -1,7 +1,7 @@
 ---
 title: "Getting Started With The Robot Simulator"
 date: "2021-06-14"
-categories: ["All", "Getting Started"]
+categories: ["Getting Started"]
 tags: []
 excerpt: "How to get started with the Micromelon Robot Simulator."
 featuredImage: "/images/resources/robot-simulator.png"
@@ -87,8 +87,6 @@ Here’s a demonstration of how to log into the simulator by connecting from the
 
 ### Doing an Activity
 
-![](/images/content/efadfd-opening-spike-drop.gif)
-
 **Selecting an Activity** Click on the activity you want to try. You will see all the details for the activity appear on the right. Some of the activities such as ** Sumo** and ** Maze** have customisation options.
 
 For this post, we’re going to pick the **Spike Drop** activity. Let’s press the ** PLAY** button.