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-beginner.mdx

@@ -1,5 +1,5 @@
 ---
-title: "Activity: Making Music (Beginner)"
+title: "Activity: Making Music I"
 date: "2024-12-31"
 categories: ["Activities", "All", "Simulator Activities"]
 tags: ["Buzzer", "Beginner", "Variables"]
@@ -27,7 +27,7 @@ Songs can be divided into a rhythm, the constant beat the music follows. Shown i
 
 Below is an example of ‘Mary Had a Little Lamb’ in sheet music. The letters have already been written below the notes. This is the example we will use for the guide, but feel free to find your own songs or even write your own music!
 
-![](/images/content/df67ce-mary-had-a-little-lamb.png)
+![](/images/content/996ff5-mary-had-a-little-lamb.png)
 
 ## Code: