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/micromelon-wins-peoples-choice-young-starters.mdx

@@ -1,10 +1,10 @@
 ---
 title: "Micromelon Wins People's Choice at Young Starters Competition"
 date: "2018-05-15"
-categories: ["All", "News & Updates"]
+categories: ["News & Updates"]
 tags: []
 excerpt: "Micromelon Robotics wins the People's Choice Award at the Young Starters competition, recognising the team's innovative approach to STEM education."
-featuredImage: "/images/awards/young-starters.png"
+featuredImage: "/images/products/rover-render.jpg"
 ---
 
 Micromelon Robotics has taken home the People's Choice Award at the Young Starters competition, a program celebrating outstanding young entrepreneurs across Queensland's startup ecosystem.