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/roaming-rover.mdx

@@ -3,6 +3,8 @@ title: "Activity: Roaming Rover"
 date: "2021-06-03"
 categories: ["Activities", "All"]
 tags: ["Iteration", "Ultrasonic", "Motors", "Beginner"]
+codingSkills: ["Iteration"]
+roverConcepts: ["Ultrasonic", "Motors"]
 excerpt: "Learn to avoid obstacles with the ultrasonic sensor."
 featuredImage: "/images/resources/roaming-rover.png"
 ---
@@ -10,53 +12,9 @@ featuredImage: "/images/resources/roaming-rover.png"
 
 Program the rover to move around the room using the ultrasonic sensor to avoid running into obstacles. If the rover detects an object, turn away from the object and keep moving forward.
 
-####
-  Relevant Coding Skills
+### Activity Demonstration
 
-    Branching
-
-	-->
-
-    Iteration
-
-    Functions
-
-    Variables
-
-	-->
-
-    Algorithm Design
-
-  -->
-
-    Maths
-
-####
-   Relevant Rover Concepts
-
-    Ultrasonic
-
-    IR
-
-	 -->
-
-    Colour
-
-    Gyroscope
-
-    Accelerometer
-
-    Motors
-
-    LEDs
-
-	-->
-
-    Buzzer
-
- 	-->
-
-Activity Demonstration
+<iframe width="560" height="315" src="https://www.youtube.com/embed/aX4v0hLU4zc" title="Roaming Rover Activity Demonstration" frameBorder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowFullScreen></iframe>
 
 ### Setup