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/binary-bot.mdx

@@ -1,8 +1,10 @@
 ---
 title: "Activity: Binary Bot"
 date: "2022-05-10"
-categories: ["Activities", "All", "Simulator Activities"]
+categories: ["Activities", "Simulator Activities"]
 tags: ["Iteration", "Motors", "Maths", "Intermediate"]
+codingSkills: ["Iteration", "Maths"]
+roverConcepts: ["Motors"]
 excerpt: "Complete a simple exercise using only binary numbers!"
 featuredImage: "/images/resources/binary-bot.png"
 ---
@@ -13,7 +15,7 @@ Complete the Driving Shapes exercise but using only binary numbers instead of de
 
 ![](/images/content/2e96eb-drivingshapes.png)
 
-Activity Demonstration
+### Activity Demonstration
 
 ### Setup