Add group invite links for easier onboarding

[vayungodara]

Problem

Joining a group requires searching or knowing the exact group name. There's no way to share a direct invite link.

What to change

• Generate unique invite codes/links per group
• Add a 'Copy Invite Link' button to group settings/details
• Create an invite landing page (e.g., /invite/[code]) that shows group info and a join button
• Handle edge cases: expired links, full groups, already-a-member
• Add invite link support to components/JoinGroupModal.js

Files to modify

• components/JoinGroupModal.js
• components/CreateGroupModal.js (show link after creation)
• New: app/invite/[code]/page.js
• Backend: API route for invite code generation and validation

Impact

Much easier group onboarding. Viral growth potential.

Effort

~4-6 hours

[vayungodara]

Closing as duplicate — kept the more detailed version.

[vayungodara]

Closing as duplicate of #18