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/chat/domain/repository.rs

@@ -0,0 +1,27 @@
+use async_trait::async_trait;
+use uuid::Uuid;
+use imphnen_utils::errors::AppError;
+use super::entity::*;
+
+#[async_trait]
+pub trait ChatRepository: Send + Sync {
+    async fn find_team_messages(&self, team_id: Uuid) -> Result<Vec<MessageWithUser>, AppError>;
+
+    async fn create_message(
+        &self,
+        id: Uuid,
+        team_id: Uuid,
+        user_id: Uuid,
+        message: &str,
+    ) -> Result<MessageEntity, AppError>;
+
+    async fn find_message_by_id(&self, id: Uuid) -> Result<Option<MessageEntity>, AppError>;
+
+    async fn delete_message(&self, id: Uuid) -> Result<bool, AppError>;
+
+    async fn get_user_info(&self, user_id: Uuid) -> Result<Option<(String, Option<String>)>, AppError>;
+
+    async fn is_team_member(&self, team_id: Uuid, user_id: Uuid) -> Result<bool, AppError>;
+
+    async fn is_team_leader(&self, team_id: Uuid, user_id: Uuid) -> Result<bool, AppError>;
+}