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/balance-bot.mdx

@@ -3,6 +3,8 @@ title: "Activity: Balance Bot"
 date: "2021-06-04"
 categories: ["Activities", "All", "Simulator Activities"]
 tags: ["Iteration", "Algorithm Design", "Accelerometer", "Motors", "Maths", "Advanced"]
+codingSkills: ["Iteration", "Algorithm Design", "Maths"]
+roverConcepts: ["Accelerometer", "Motors"]
 excerpt: "Learn iteration, algorithm design, maths, and how to use the Rover’s accelerometer and motors."
 featuredImage: "/images/resources/balance-bot.png"
 ---
@@ -10,53 +12,9 @@ featuredImage: "/images/resources/balance-bot.png"
 
 Challenge students to program their rover to always try and stabilise itself. When complete, the rover will always turn and drive upwards on any tilted surface. Once the surface the robot is driving on is flat, it should stop moving. This means the robot will balance on a seesaw. Students will need to use data from the accelerometer to control the motors based on the orientation of the rover.
 
-####
-  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/X428Usiv-qY" title="Balance Bot Activity Demonstration" frameBorder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowFullScreen></iframe>
 
 ### Setup