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/guide-how-to-design-a-rover-attachment.mdx

@@ -27,9 +27,9 @@ Here at Micromelon, we’ve already gone ahead and made a few attachments for yo
 
                       Claw
 
-![](/images/content/f68538-img_1131.jpg)
+![](/images/content/5400a3-img_1131.jpg)
 
-![](/images/content/f68538-img_1131.jpg)
+![](/images/content/5400a3-img_1131.jpg)
 
                       Roborave Line Follow
 
@@ -39,37 +39,31 @@ Here at Micromelon, we’ve already gone ahead and made a few attachments for yo
 
                       Ping-Pong Shooter
 
-![](/images/content/c43f17-img_0655.jpg)
+![](/images/content/47ffe1-img_0655.jpg)
 
-![](/images/content/c43f17-img_0655.jpg)
+![](/images/content/47ffe1-img_0655.jpg)
 
                       Tipper
 
-![](/images/content/d2c474-img_0469.jpg)
+![](/images/content/0827d5-img_0469.jpg)
 
-![](/images/content/d2c474-img_0469.jpg)
+![](/images/content/0827d5-img_0469.jpg)
 
                       Whiteboard Marker Holder
 
-![](/images/content/9b3b36-img_0458.jpg)
-
-![](/images/content/9b3b36-img_0458.jpg)
-
                       Seed Planter
 
 ![](/images/content/7ebf65-img_0822.jpg)
 
 ![](/images/content/2aa593-final.jpg)
 
-![](/images/content/f68538-img_1131.jpg)
+![](/images/content/5400a3-img_1131.jpg)
 
 ![](/images/content/72c1a3-img_1117.jpg)
 
-![](/images/content/c43f17-img_0655.jpg)
+![](/images/content/47ffe1-img_0655.jpg)
 
-![](/images/content/d2c474-img_0469.jpg)
-
-![](/images/content/9b3b36-img_0458.jpg)
+![](/images/content/0827d5-img_0469.jpg)
 
 For further information about our existing attachments, visit our page on rover expansions.[Rover Expansions & 3D Printing](/rover-expansion-3d-printing)