feat: migrate imphnen-backend-hackathon into workspace as imphnen-hackathon crate

Consolidates the standalone hackathon backend (16 crates) into a single
imphnen-hackathon crate following the existing clean architecture patterns.
All endpoints are exposed under /v1/hackathon/ via the gateway.

Features migrated:
- Auth: Supabase-based signup/login/GitHub OAuth/password reset (own JWT)
- Users: profile management with team listing
- Teams: CRUD with city validation, deadline enforcement, invite system
- Invitations: team member invitations with accept/reject flow
- Join Requests: team join request workflow
- Chat: team messaging with author/leader delete permissions
- Submissions: project submission lifecycle (draft→pending→submitted)
- Storage: Supabase Storage file upload endpoints
- Certificates: public user certificate data endpoint
- Winners: public winners listing
- Admin: admin-only CRUD for all entities

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

imphnen-hackathon/src/invitations/domain/repository.rs

@@ -0,0 +1,41 @@
+use async_trait::async_trait;
+use uuid::Uuid;
+use imphnen_utils::errors::AppError;
+use super::entity::*;
+
+#[async_trait]
+pub trait InvitationRepository: Send + Sync {
+    async fn create(
+        &self,
+        invitation_id: Uuid,
+        team_id: Uuid,
+        inviter_id: Uuid,
+        invitee_email: &str,
+    ) -> Result<InvitationEntity, AppError>;
+
+    async fn find_by_id(&self, id: Uuid) -> Result<Option<InvitationEntity>, AppError>;
+
+    async fn find_pending_by_email(&self, email: &str) -> Result<Vec<InvitationWithDetails>, AppError>;
+
+    async fn update_status(&self, id: Uuid, status: &str) -> Result<(), AppError>;
+
+    async fn reject_pending_for_email_except(&self, email: &str, except_id: Uuid) -> Result<(), AppError>;
+
+    async fn add_team_member(&self, team_id: Uuid, user_id: Uuid) -> Result<(), AppError>;
+
+    async fn reject_pending_join_requests_for_user(&self, user_id: Uuid) -> Result<(), AppError>;
+
+    async fn get_team_leader_id(&self, team_id: Uuid) -> Result<Option<Uuid>, AppError>;
+
+    async fn get_team_name(&self, team_id: Uuid) -> Result<Option<String>, AppError>;
+
+    async fn get_user_email(&self, user_id: Uuid) -> Result<Option<String>, AppError>;
+
+    async fn get_inviter_name(&self, user_id: Uuid) -> Result<Option<String>, AppError>;
+
+    async fn active_member_count(&self, team_id: Uuid) -> Result<i64, AppError>;
+
+    async fn team_has_submission(&self, team_id: Uuid) -> Result<bool, AppError>;
+
+    async fn user_active_team_name(&self, user_id: Uuid) -> Result<Option<String>, AppError>;
+}