feat(frontend): add remove button to pending and submitted file cards

Lets users drop an uploaded file from the UI list before or after
conversion, without cancelling anything server-side.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

frontend/src/locales/en.json

@@ -1,5 +1,8 @@
 {
   "brand": "Ombrora Convert",
+  "common": {
+    "remove": "Remove"
+  },
   "nav": {
     "switchToEnglish": "English",
     "switchToFrench": "Français",

frontend/src/locales/fr.json

@@ -1,5 +1,8 @@
 {
   "brand": "Ombrora Convert",
+  "common": {
+    "remove": "Supprimer"
+  },
   "nav": {
     "switchToEnglish": "English",
     "switchToFrench": "Français",