Audit and improve lessons and practices for clarity and to improve student understanding

This is a bit of a more long-term issue that I'm writing down for a future reference. I want to review all lessons and practices in Learn GDScript to address several recurring issues that affect student comprehension. This is about a review that should be done systematically across the entire app.

Here are the areas to address:

**Missing code execution context**

Practices don't necessarily show or explain how the app will execute and test the student's code. This leaves students feeling lost, especially when:

- They need to write functions with specific parameters
- They're unsure when or how their function will be called
- They don't understand how the app will interact with their code

I've patched some but this needs a thorough review.

**Lesson recaps and expectation**

Students need regular checkpoints to understand their progress and set realistic expectations. Common issues include:

- Students wanting to make complete games immediately after finishing the app (they've only learned coding basics for a few hours)
- Students worrying that concepts aren't perfectly clear the first time they've been exposed to it.

Every concept will need them to practice and review/revisit multiple times across their projects and throughout learning to fully understand

For that we should add regular recap sections in lessons that:

- Summarize what students should understand at this point
- Clarify that it's perfectly normal not to fully understand yet
- Reassure students that some concepts are tricky and will need multiple encounters to click
- Help students set realistic expectations about their skill level

For example, "Don't worry if for loops aren't completely clear yet. They're a tricky concept that takes time to master. You'll understand them better as you practice more."

Related: #1189

**For loops improvements**

Students are frequently confused by for loops. We need to make these lessons clearer.

- Review all for loop lessons
- Add more relatable examples (for instance, show equivalent examples using familiar variable names like "cat" instead of just numbers)
- Consider adding more step-by-step breakdowns of how for loops execute or visualizations to illustrate the concept better