Consistent hero layouts, activity page redesign, new content, and YouTube embeds

- Product pages (Code Editor, Robot Simulator): text-left/image-right hero layout
- Related resources capped at 3 items on all product pages
- Making Music activities renamed to I, II, III
- New Maze I/II/III and Sumo I/II/III difficulty-graded activities
- YouTube demo videos restored on 12 activity pages from old site
- Activity pages: two-column hero with coding skills & rover concepts tags
- Blog/news pages: same two-column hero layout with date
- Resource type extended with codingSkills, roverConcepts, tags fields
- Removed raw "Relevant Coding Skills/Rover Concepts" text from activity MDX

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

content/resources/activity-making-music-intermediate.mdx

@@ -1,5 +1,5 @@
 ---
-title: "Activity: Making Music (Intermediate)"
+title: "Activity: Making Music II"
 date: "2024-12-30"
 categories: ["Activities", "All", "Simulator Activities"]
 tags: ["Intermediate", "Variables", "Buzzer", "Iteration"]
@@ -23,7 +23,7 @@ When it comes to reading sheet music for this task, we will be using two pieces
 
 ![](/images/content/384e17-rhythm.jpg)
 
-![](/images/content/c40deb-mary-had-a-little-lamb.png)
+![](/images/content/996ff5-mary-had-a-little-lamb.png)
 
 ## Code: