🐛 Return 400 instead of 500 when ImageMagick fails on invalid images (#10643)

When ImageMagick fails to process an uploaded image (e.g., corrupted PNG
with invalid IHDR data), the backend was raising :type :internal with
:code :imagemagick-error, which mapped to HTTP 500. The frontend treated
this as a server error and displayed the full error page.

Changed exec-magick! to raise :type :validation with :code :invalid-image
instead. This flows through the existing :invalid-image handler in
errors.clj which returns HTTP 400. The frontend's handle-media-error and
process-error now catch this code and show a notification banner.

AI-assisted-by: qwen3.7-plus

backend/src/app/media.clj

@@ -184,8 +184,8 @@
                             :env (get-imagemagick-env)
                             :timeout 60)]
     (when (not= 0 (:exit result))
-      (ex/raise :type :internal
-                :code :imagemagick-error
+      (ex/raise :type :validation
+                :code :invalid-image
                 :hint (str "ImageMagick command failed: " (:err result))
                 :cmd cmd
                 :exit (:exit result)))

backend/test/backend_tests/media_test.clj

@@ -67,8 +67,8 @@
         (t/is false "should have thrown")
         (catch Exception e
           (let [data (ex-data e)]
-            ;; Could be validation or imagemagick-error depending on what magick does
-            (t/is (contains? #{:validation :internal} (:type data)))))
+            (t/is (= :validation (:type data)))
+            (t/is (= :invalid-image (:code data)))))
         (finally
           (fs/delete path))))))
 

frontend/src/app/main/data/media.cljs

@@ -70,6 +70,9 @@
               (= (:code error) :media-type-mismatch)
               (tr "errors.media-type-mismatch")
 
+              (= (:code error) :invalid-image)
+              (tr "errors.media-type-not-allowed")
+
               :else
               (tr "errors.unexpected-error"))]
     (rx/of (ntf/error msg))))