fixed invalid post title breaking links

backend/src/handlers/posts.rs

@@ -115,16 +115,22 @@ pub async fn create_post(
         return Err(AppError::Unauthorized);
     }
 
-    validate_slug(&payload.slug)?;
+    let slug = slug::slugify(&payload.slug);
+    if slug.is_empty() {
+        return Err(AppError::BadRequest(
+            "Slug is empty after normalization (try ASCII letters/numbers)".to_string(),
+        ));
+    }
+    validate_slug(&slug)?;
     if let Some(ref old) = payload.old_slug {
         validate_slug(old)?;
     }
 
     let posts_dir = state.data_dir.join("posts");
-    let file_path = posts_dir.join(format!("{}.md", payload.slug));
+    let file_path = posts_dir.join(format!("{}.md", slug));
 
     if let Some(ref old_slug) = payload.old_slug {
-        if old_slug != &payload.slug {
+        if old_slug != &slug {
             let old_path = posts_dir.join(format!("{}.md", old_slug));
             if old_path.exists() {
                 if file_path.exists() {
@@ -134,11 +140,11 @@ pub async fn create_post(
                 }
                 let _guard = state.post_lock.lock().await;
                 fs::rename(&old_path, &file_path).map_err(|e| {
-                    error!("Rename error from {} to {}: {}", old_slug, payload.slug, e);
+                    error!("Rename error from {} to {}: {}", old_slug, slug, e);
                     AppError::Internal("Rename error".to_string(), Some(e.to_string()))
                 })?;
                 drop(_guard);
-                info!("Renamed post from {} to {}", old_slug, payload.slug);
+                info!("Renamed post from {} to {}", old_slug, slug);
             }
         }
     }
@@ -150,11 +156,11 @@ pub async fn create_post(
         draft: payload.draft,
     };
     let contents = serialize_post(&meta, &payload.content)?;
-    write_post_atomic(&state, &payload.slug, &contents).await?;
+    write_post_atomic(&state, &slug, &contents).await?;
 
-    info!("Post saved: {}", payload.slug);
+    info!("Post saved: {}", slug);
     Ok(Json(PostDetail {
-        slug: payload.slug,
+        slug,
         date: meta.date,
         summary: meta.summary,
         tags: meta.tags,