feat: Add "The Mango Harvest (For Loops)" Case Study Module

[akshatsharma941]

This PR introduces The Mango Harvest, a standalone, interactive case study module for the PyBe platform designed to teach Python for loops.

Following PyBe's core philosophy - that the situation must earn the construct - this module uses Constructivist and Cognitive Load Theory principles to bypass the heavy cognitive load of abstract syntax. Instead of starting with code, learners are immersed in a relatable narrative (Dada harvesting a mango orchard) guided by a Socratic observer (The Fox).

Key Learner Benefits:

1. Concrete-to-Abstract Progression: Learners experience sequential processing visually and interactively before ever seeing a line of Python code.
2. Intuitive Analogical Transfer: By mapping the orchard to a list and the individual tree to a loop variable, the mechanics of iteration (the "Conveyor Belt" mental model) become immediately obvious.
3. Scaffolded Practice: Includes a drag-and-drop block coding activity, allowing learners to focus on structural logic without being punished for minor syntax errors.
4. Socratic & Non-Punitive: Misconceptions are gently addressed through targeted, penalty-free assessments that guide the learner toward the right answer rather than grading them.

Technical Details:

1. Built as a lightweight, offline-first Single Page Application (SPA).
2. Uses purely Vanilla HTML, CSS, and JS (no framework, no build step required).
3. Unidirectional state management via a custom lessonEngine.js.
4. Fully conforms to the PyBe platform's accessibility and design system standards outlined in the Team Product Document.

How to test:

1. Clone the repository and navigate to summership-26-prs/Akshat Sharma/.
2. Start a local server (e.g., python -m http.server 8000).
3. Open http://localhost:8000 to verify the module's interactive flow and offline capabilities.