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/join_requests/infrastructure/http/dto.rs

@@ -0,0 +1,50 @@
+use serde::{Deserialize, Serialize};
+use utoipa::ToSchema;
+use uuid::Uuid;
+use chrono::{DateTime, Utc};
+use crate::join_requests::domain::entity::*;
+
+#[derive(Debug, Serialize, Deserialize, ToSchema)]
+pub struct JoinRequestResponse {
+    pub id: Uuid,
+    pub team_id: Uuid,
+    pub user_id: Uuid,
+    pub user_fullname: String,
+    pub user_email: String,
+    pub user_avatar: Option<String>,
+    pub message: String,
+    pub status: String,
+    pub created_at: Option<DateTime<Utc>>,
+}
+
+impl From<JoinRequestWithDetails> for JoinRequestResponse {
+    fn from(e: JoinRequestWithDetails) -> Self {
+        Self {
+            id: e.id,
+            team_id: e.team_id,
+            user_id: e.user_id,
+            user_fullname: e.user_fullname,
+            user_email: e.user_email,
+            user_avatar: e.user_avatar,
+            message: e.message,
+            status: e.status,
+            created_at: e.created_at,
+        }
+    }
+}
+
+#[derive(Debug, Serialize, Deserialize, ToSchema)]
+pub struct CreateJoinRequestRequest {
+    pub message: String,
+}
+
+impl From<CreateJoinRequestRequest> for CreateJoinRequestInput {
+    fn from(r: CreateJoinRequestRequest) -> Self {
+        Self { message: r.message }
+    }
+}
+
+#[derive(Debug, Serialize, Deserialize, ToSchema)]
+pub struct RespondToJoinRequestRequest {
+    pub accept: bool,
+}