fix(curriculum): correct object reference and method binding explanations - #71488

Checklist:

• I have read and followed the contribution guidelines.
• I have read and followed the how to open a pull request guide.
• My pull request targets the main branch of freeCodeCamp.
• I have tested these changes either locally on my machine, or GitHub Codespaces.

Closes #71481

Summary of Changes

1. Primitive vs. Non-Primitive Data Types Lesson (6732b73d25cc01251b778043.md):

   • Corrected the description of assigning an object reference to avoid calling it "shallow copying by reference".
   • Clarified that this operation copies the reference without creating a new outer object, distinguishing it from a shallow copy.
   • Updated both the JavaScript v9 and Front-End Development copies.

2. Functions vs. Object Methods Lesson (6732b749b8aad125523dcda5.md):

   • Clarified that invoking a method with dot notation (e.g. person.sayHello()) supplies person as the value of this.
   • Removed the inaccurate claim that ordinary methods are permanently bound to the object where they were defined.
   • Updated both the JavaScript v9 and Front-End Development copies.