fix: Resolve 75 compile errors across 13 backend files

Remove deprecated #[axum::async_trait] from 2 middleware files (native
async traits on Rust 1.88+). Fix 71 stub handlers: change return type
from ApiResult<impl IntoResponse> to ApiResult<Json<Value>> and replace
todo!() with proper JSON stub responses. Clean compile, zero errors.

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

backend/src/api/wipes.rs

@@ -2,7 +2,7 @@ use std::sync::Arc;
 
 use axum::{
     routing::{get, post},
-    Router,
+    Json, Router,
 };
 
 use crate::models::error::ApiResult;
@@ -18,26 +18,26 @@ pub fn router() -> Router<Arc<AppState>> {
         .route("/history/{id}", get(get_wipe_history_detail))
 }
 
-async fn trigger_wipe() -> ApiResult<impl axum::response::IntoResponse> {
-    todo!()
+async fn trigger_wipe() -> ApiResult<Json<serde_json::Value>> {
+    Ok(Json(serde_json::json!({"status": "not_implemented"})))
 }
 
-async fn dry_run_wipe() -> ApiResult<impl axum::response::IntoResponse> {
-    todo!()
+async fn dry_run_wipe() -> ApiResult<Json<serde_json::Value>> {
+    Ok(Json(serde_json::json!({"status": "not_implemented"})))
 }
 
-async fn rollback_wipe() -> ApiResult<impl axum::response::IntoResponse> {
-    todo!()
+async fn rollback_wipe() -> ApiResult<Json<serde_json::Value>> {
+    Ok(Json(serde_json::json!({"status": "not_implemented"})))
 }
 
-async fn get_wipe_status() -> ApiResult<impl axum::response::IntoResponse> {
-    todo!()
+async fn get_wipe_status() -> ApiResult<Json<serde_json::Value>> {
+    Ok(Json(serde_json::json!({"status": "not_implemented"})))
 }
 
-async fn get_wipe_history() -> ApiResult<impl axum::response::IntoResponse> {
-    todo!()
+async fn get_wipe_history() -> ApiResult<Json<serde_json::Value>> {
+    Ok(Json(serde_json::json!({"status": "not_implemented"})))
 }
 
-async fn get_wipe_history_detail() -> ApiResult<impl axum::response::IntoResponse> {
-    todo!()
+async fn get_wipe_history_detail() -> ApiResult<Json<serde_json::Value>> {
+    Ok(Json(serde_json::json!({"status": "not_implemented"})))
 }