docs: add initial product requirements document

[GTPSHAX]

Summary

This PR introduces a comprehensive Product Requirements Document (PRD) for the Modul Ajar Generator project. This documentation serves as the foundational blueprint for the application, aligning stakeholders and developers on the product vision, core functionalities, and technical architecture required to support PAUD teachers.

Key Changes

• Product Documentation: Created a detailed PRD covering the project vision, problem statement, and strategic goals.
• Requirements Definition: Detailed both functional requirements (AI autofill, DOCX generation) and technical specifications (OpenAI integration, VM-based processing, hCaptcha validation).
• User Journey Mapping: Outlined the end-to-end teacher experience, focusing on accessibility for users with low digital literacy.
• System Architecture Visuals: Included Mermaid sequence diagrams to illustrate complex backend flows, specifically for the AI suggestion engine and the document generation pipeline.
• Strategic Planning: Defined project constraints, measurable success criteria (KPIs), and a risk mitigation framework.

Why this is necessary

The project has reached a level of technical complexity that requires a single source of truth to prevent "scope creep" and ensure architectural consistency.

1. Alignment: Ensures that the development of the "Modul Ajar" systems follows a unified vision.
2. Accessibility Focus: By documenting the user journey for PAUD teachers, we ensure that technical decisions (like AI autofill) directly solve the digital literacy barrier.
3. Technical Clarity: Sequence diagrams help developers understand the interaction between the Laravel control plane, AI handlers, and the document generation service.

How to Test

1. Documentation Review: Access the newly added PRD.md (or relevant documentation folder) and verify that all sections (Vision, Journey, Technical, Risks) are complete.
2. Diagram Rendering: Ensure that the Mermaid sequence diagrams render correctly in your Markdown previewer or GitHub interface.
3. Logic Cross-Reference: Compare the technical requirements in the PRD against the current implementation of handle-generate-docx.js and handle-autofill-ai.js to ensure alignment.