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/balloon-battle-bots-at-trinity-college-beenleigh.mdx

@@ -1,7 +1,7 @@
 ---
 title: "Balloon Battle Bots at Trinity College Beenleigh"
 date: "2022-08-05"
-categories: ["Customer Stories", "All"]
+categories: ["Customer Stories"]
 tags: []
 excerpt: "Last year supported by ACS and the Gateway to Industry Schools ICT program Trinity College and Micromelon started their first Balloon Battle Bots Competition.Using the Micromelon Rovers students learnt to program their robots in Blocks and Python, be"
 featuredImage: "/images/resources/balloon-battle-bots-at-trinity-college-beenleigh.jpeg"