[Phase 6] Add group.types.ts and group.service.ts

[MohamedRamadanSaudi]

Task

Create frontend/src/types/group.types.ts and frontend/src/services/api/group.service.ts.

Types

Group, GroupMember, GroupRole, GroupInvitation, GroupSession, ChatMessage

Service methods

• Group CRUD: getMyGroups, getGroup, createGroup, updateGroup, deleteGroup
• Members: getMembers, updateMemberRole, removeMember, leaveGroup
• Invitations: sendInvitation, listInvitations, cancelInvitation, getInvitationInfo, acceptInvitation
• Sessions: getGroupSessions, getGroupSession
• Chatbot: sendChatMessage