- Added route + handler: GenerateInviteLinkHandler to create signed tokens
- Added handler: JoinSyndicateWithTokenHandler to join using invite token
- Integrated secure token generation via helpers.GenerateSecureToken()
- Created DB model: syndicate_invite_tokens (assumed pre-existing)
- Updated syndicate view template to allow managers to generate links
- Flash messaging for invite success/failure
- Invite links are scoped to manager role and valid for 48 hours
- Implemented `CreateSyndicate` with transaction support
- Added `InviteToSyndicate` with membership check and invite insert
- Created syndicate invite model and DB logic for accepting/declining
- Ensured consistent error handling with `fmt.Errorf`
- Cleaned up unused invite handlers/routes
- Added `RestoreMessageHandler` and route at `/account/messages/restore`
- Updated `users_messages` table to support `archived_at` reset
- Added restore button to archived messages template
- Ensures archived messages can be moved back into inbox
