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/handlers.rs

@@ -0,0 +1,47 @@
+use axum::{Extension, Json, extract::Path, response::IntoResponse};
+use std::sync::Arc;
+use uuid::Uuid;
+use imphnen_utils::{errors::AppError, response_format::{ApiSuccess, ApiMessage}};
+use crate::middleware::hackathon_auth::HackathonAuthUser;
+use crate::join_requests::domain::service::JoinRequestService;
+use super::dto::*;
+
+pub async fn create_join_request_handler(
+    Extension(service): Extension<Arc<dyn JoinRequestService>>,
+    Extension(auth): Extension<HackathonAuthUser>,
+    Path(team_id): Path<Uuid>,
+    Json(body): Json<CreateJoinRequestRequest>,
+) -> Result<axum::response::Response, AppError> {
+    let request = service.create_join_request(team_id, auth.user_id, body.into()).await?;
+    Ok(ApiSuccess(JoinRequestResponse::from(request)).into_response())
+}
+
+pub async fn get_my_join_requests_handler(
+    Extension(service): Extension<Arc<dyn JoinRequestService>>,
+    Extension(auth): Extension<HackathonAuthUser>,
+) -> Result<axum::response::Response, AppError> {
+    let list = service.get_my_join_requests(auth.user_id).await?;
+    let response: Vec<JoinRequestResponse> = list.into_iter().map(JoinRequestResponse::from).collect();
+    Ok(ApiSuccess(response).into_response())
+}
+
+pub async fn get_team_join_requests_handler(
+    Extension(service): Extension<Arc<dyn JoinRequestService>>,
+    Extension(auth): Extension<HackathonAuthUser>,
+    Path(team_id): Path<Uuid>,
+) -> Result<axum::response::Response, AppError> {
+    let list = service.get_team_join_requests(team_id, auth.user_id).await?;
+    let response: Vec<JoinRequestResponse> = list.into_iter().map(JoinRequestResponse::from).collect();
+    Ok(ApiSuccess(response).into_response())
+}
+
+pub async fn respond_to_join_request_handler(
+    Extension(service): Extension<Arc<dyn JoinRequestService>>,
+    Extension(auth): Extension<HackathonAuthUser>,
+    Path(request_id): Path<Uuid>,
+    Json(body): Json<RespondToJoinRequestRequest>,
+) -> Result<axum::response::Response, AppError> {
+    service.respond_to_join_request(request_id, auth.user_id, body.accept).await?;
+    let msg = if body.accept { "Join request accepted" } else { "Join request rejected" };
+    Ok(ApiMessage::ok(msg).into_response())
+}