feat: collaborative learning spaces and peer tutoring GSSoC

[Akshita-2307]

Summary

Implements collaborative learning spaces and peer tutoring system for VidyaSetu.

Changes

Prisma Schema

• StudyGroup - groups for collaborative study with named membership
• GroupMember - many-to-many membership with roles (OWNER/MODERATOR/MEMBER)
• TutoringRequest - peer tutoring requests from students to tutors
• TutoringSession - scheduled one-on-one tutoring sessions with status tracking
• Enums: GroupRole, TutoringStatus, SessionStatus
• Relations added to User and Subject models

Backend Module (modules/collaboration/)

• types - DTOs: StudyGroupDTO, StudyGroupDetailDTO, TutoringRequestDTO, TutoringSessionDTO, CollaborationSummary
• validator - Zod schemas for all create/update operations
• repository - Prisma queries with proper pagination and relations
• service - business logic for group membership, request lifecycle, session scheduling
• controller - request handling with auth context
• index - barrel exports

API Routes

• GET/POST /api/collaboration/groups - list/create groups
• GET/DELETE /api/collaboration/groups/[id] - group detail / leave
• POST /api/collaboration/groups/join - join a group
• GET/POST /api/collaboration/requests - tutoring requests
• PATCH /api/collaboration/requests/[id] - accept/cancel request
• GET/POST /api/collaboration/sessions - tutoring sessions
• PATCH /api/collaboration/sessions/[id] - update session status
• GET /api/collaboration/summary - user dashboard stats

Frontend Pages

• /collaboration - dashboard with summary cards and quick links
• /collaboration/groups - group listing with create/join
• /collaboration/groups/[groupId] - group detail with members
• /collaboration/tutoring - request tutoring, manage incoming/outgoing requests
• /collaboration/sessions - schedule/manage tutoring sessions with status transitions

Client Library

• lib/collaboration.ts - typed authFetch wrapper for all endpoints

Fixes

• Next.js 16 route handler params type (now Promise)
• TypeScript cast pre-existing errors in quiz pages

Security

• All routes use SetCookies.verifyCookies() for auth
• Group membership verified before operations
• Users can only manage their own requests/sessions

Closes #273

GSSoC

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