feat: batch favorites endpoint + frontend dedup fixes

Backend:
- Add POST /api/favorites/batch endpoint (single multi-row INSERT)
- Add BatchFavoritesResult/BatchFavoritesStats DTOs
- Add batch methods to ports, service, PG repository
- Transaction-based insert with ON CONFLICT DO NOTHING, chunking at 5000

Frontend:
- Rewrite batchFavorites() to single API call (40 requests → 1)
- Add _replaceCacheFromResponse() to avoid extra GET round-trip
- Centralize formatFileSize, isTextViewable, formatDateTime, formatDateShort
- Remove duplicate icon mapping from app.js
- Fix inconsistent quota defaults (10GB everywhere)

src/interfaces/api/handlers/favorites_handler.rs

@@ -1,15 +1,24 @@
-use axum::{
-    Json,
-    extract::{Path, State},
-    http::StatusCode,
-    response::IntoResponse,
-};
+use axum::{Json, extract::{Path, State}, http::StatusCode, response::IntoResponse};
+use serde::Deserialize;
 use std::sync::Arc;
 use tracing::{error, info};
 
 use crate::application::ports::favorites_ports::FavoritesUseCase;
 use crate::interfaces::middleware::auth::AuthUser;
 
+/// Single item in a batch-add-favorites request.
+#[derive(Debug, Deserialize)]
+pub struct BatchFavoriteItem {
+    pub item_id: String,
+    pub item_type: String,
+}
+
+/// Request body for POST /api/favorites/batch
+#[derive(Debug, Deserialize)]
+pub struct BatchFavoritesRequest {
+    pub items: Vec<BatchFavoriteItem>,
+}
+
 /// Handler for favorite-related API endpoints
 pub async fn get_favorites(
     State(favorites_service): State<Arc<dyn FavoritesUseCase>>,
@@ -120,3 +129,63 @@ pub async fn remove_favorite(
         }
     }
 }
+
+/// Add multiple items to favourites in a single transaction.
+/// POST /api/favorites/batch
+pub async fn batch_add_favorites(
+    State(favorites_service): State<Arc<dyn FavoritesUseCase>>,
+    auth_user: AuthUser,
+    Json(body): Json<BatchFavoritesRequest>,
+) -> impl IntoResponse {
+    let user_id = &auth_user.id;
+
+    if body.items.is_empty() {
+        return (
+            StatusCode::BAD_REQUEST,
+            Json(serde_json::json!({ "error": "items array must not be empty" })),
+        )
+            .into_response();
+    }
+
+    // Validate item types
+    for item in &body.items {
+        if item.item_type != "file" && item.item_type != "folder" {
+            return (
+                StatusCode::BAD_REQUEST,
+                Json(serde_json::json!({
+                    "error": format!("Item type must be 'file' or 'folder', got '{}'", item.item_type)
+                })),
+            )
+                .into_response();
+        }
+    }
+
+    let items: Vec<(String, String)> = body
+        .items
+        .into_iter()
+        .map(|i| (i.item_id, i.item_type))
+        .collect();
+
+    match favorites_service
+        .batch_add_to_favorites(user_id, &items)
+        .await
+    {
+        Ok(result) => {
+            info!(
+                "Batch favourites: {} requested, {} inserted, {} already existed",
+                result.stats.requested, result.stats.inserted, result.stats.already_existed
+            );
+            (StatusCode::OK, Json(serde_json::json!(result))).into_response()
+        }
+        Err(err) => {
+            error!("Error in batch add favorites: {}", err);
+            (
+                StatusCode::INTERNAL_SERVER_ERROR,
+                Json(serde_json::json!({
+                    "error": format!("Failed to batch add favorites: {}", err)
+                })),
+            )
+                .into_response()
+        }
+    }
+}