feat: upload drag-drop + responsive mobile

Backend:
- Route POST /api/upload avec multipart (axum 0.8)
- Proxy vers Imago, validation MIME, feedback JSON

Frontend:
- Zone de drop avec drag & drop (effet visuel au survol)
- Bouton Upload dans le header + FAB flottant mobile
- Support Ctrl+V (coller depuis presse-papier)
- Upload multiple, feedback toast (succès/erreur)
- Raccourci Ctrl+U pour upload
- Responsive: 2 breakpoints (768px, 400px)
- Gallery 2 colonnes sur mobile, FAB, toasts bottom
- user-scalable=no, tap-highlight transparent

src/server/routes.rs

@@ -1,8 +1,8 @@
 //! Routes API REST du dashboard — proxy vers Imago v2
 
 use axum::{
-    Router, routing::get,
-    extract::{Path, Query, State},
+    Router, routing::{get, post},
+    extract::{Multipart, Path, Query, State},
     response::IntoResponse,
     Json,
 };
@@ -55,6 +55,7 @@ pub fn api_routes(state: AppState) -> Router {
     let state = Arc::new(state);
     Router::new()
         .route("/api/health", get(health_check))
+        .route("/api/upload", post(upload_image))
         .route("/api/images", get(list_images))
         .route("/api/images/search", get(search_images))
         .route("/api/images/{id}", get(get_image))
@@ -69,6 +70,65 @@ async fn health_check() -> &'static str {
     "OK"
 }
 
+/// Upload d'image : reçoit un fichier et le transmet à l'API Imago
+async fn upload_image(
+    State(state): State<Arc<AppState>>,
+    mut multipart: Multipart,
+) -> impl IntoResponse {
+    let mut data: Vec<u8> = Vec::new();
+    let mut filename = String::from("upload.png");
+    let mut mime_type = String::from("image/png");
+
+    while let Ok(Some(mut field)) = multipart.next_field().await {
+        let name = field.name().unwrap_or("").to_string();
+        if name == "file" {
+            if let Some(fn_) = field.file_name() {
+                filename = fn_.to_string();
+            }
+            if let Some(mt) = field.content_type() {
+                mime_type = mt.to_string();
+            }
+            while let Ok(Some(chunk)) = field.chunk().await {
+                data.extend_from_slice(&chunk);
+            }
+        }
+    }
+
+    if data.is_empty() {
+        return (
+            axum::http::StatusCode::BAD_REQUEST,
+            Json(serde_json::json!({"error": "Aucun fichier reçu"})),
+        );
+    }
+
+    // Validation MIME basique côté dashboard
+    if !mime_type.starts_with("image/") {
+        return (
+            axum::http::StatusCode::UNSUPPORTED_MEDIA_TYPE,
+            Json(serde_json::json!({"error": format!("Type MIME non supporté : {}", mime_type)})),
+        );
+    }
+
+    match state.imago.upload_image(data, &filename, None).await {
+        Ok(response) => (
+            axum::http::StatusCode::CREATED,
+            Json(serde_json::json!({
+                "id": response.id,
+                "uuid": response.uuid,
+                "filename": response.original_name,
+                "status": response.status,
+            })),
+        ),
+        Err(e) => {
+            tracing::error!("Upload vers Imago échoué : {:#}", e);
+            (
+                axum::http::StatusCode::BAD_GATEWAY,
+                Json(serde_json::json!({"error": format!("Échec de l'upload : {:#}", e)})),
+            )
+        }
+    }
+}
+
 async fn list_images(
     State(state): State<Arc<AppState>>,
     Query(pagination): Query<Pagination>,