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/activity-making-music-advanced.mdx

@@ -1,8 +1,10 @@
 ---
 title: "Activity: Making Music III"
 date: "2024-12-31"
-categories: ["Activities", "All", "Simulator Activities"]
+categories: ["Activities", "Simulator Activities"]
 tags: ["Iteration", "Buzzer", "Algorithm Design", "Variables", "Advanced"]
+codingSkills: ["Iteration", "Algorithm Design", "Variables"]
+roverConcepts: ["Buzzer"]
 excerpt: "Use the Rovers speaker to make it play songs. Learn to combine the world of music and robotics by going through sheet music and coding the Rover to play each note.In the advanced code, we will make a system to allow us to write our enti"
 featuredImage: "/images/resources/activity-making-music-advanced.jpg"
 ---
@@ -13,7 +15,7 @@ In the advanced code, we will make a system to allow us to write our entire song
 
 ![](/images/content/40dff0-img_1856.jpg)
 
-Activity Demonstration
+### Activity Demonstration
 
 ### Basics of Music:
 
@@ -21,10 +23,6 @@ When it comes to reading sheet music for this task, we will be using two pieces
 
 ![](/images/content/6babfe-notes.png)
 
-![](/images/content/384e17-rhythm.jpg)
-
-![](/images/content/996ff5-mary-had-a-little-lamb.png)
-
 ## Code:
 
 We will switch to the text code editor for the intermediate and advanced music activities as some of the following functions are easier to build in that editor. Unfortunately the block editor cannot be used for this code as we will be using python dictionaries which are incompatible with blocks.