docs(onboarding): add ONBOARDING-Subhajit-Samajpati.md

[Crypticfr]

Summary

Added the mandatory contributor onboarding document Ideas/ONBOARDING-Subhajit-Samajpati.md.

Document Overview

• 1. What is FLN: Overview of Foundational Literacy and Numeracy, multi-grade teaching challenges, and why a paper-first scanning system is needed.
• 2. FLN as a System: Explains the 7 user roles (Teachers, Volunteers, Principals, Admins, Superadmins) and how paper generation, scanning, and evaluations connect.
• 3. Current State of the Repository: Tech stack overview (React 19, TypeScript, Express, MongoDB Atlas, Python OCR pipeline).
• 4. Gaps Observed in the Code: Identifies 5 gaps (no daily attendance roll-call, static curriculum files without in-app preview, plain CSV logbook exports, missing location data in JWTs, and unhandled sub-panel errors).
• 5. Ideas for the Project: Proposed solutions (Daily Attendance Tracker, 93-Level Content Library Modal, formatted Excel .xlsx exports, better JWT scoping, and React Error Boundaries).
• 6. Contribution: Details implemented features across attendance, content preview, Excel exports, authentication, and build validation.

Files Changed

• Ideas/ONBOARDING-Subhajit-Samajpati.md (Added onboarding document)