[web] Add missing translation

web-src/src/i18n/de.json

@@ -36,6 +36,7 @@
         "loading": "Lade…",
         "placeholder": "https://url-to-stream",
         "play": "Spielen",
+        "processing": "Verarbeite…",
         "title": "Stream hinzufügen"
       }
     },

web-src/src/i18n/en.json

@@ -36,6 +36,7 @@
         "loading": "Loading…",
         "placeholder": "https://url-to-stream",
         "play": "Play",
+        "processing": "Processing…",
         "title": "Add stream"
       }
     },

web-src/src/i18n/fr.json

@@ -36,6 +36,7 @@
         "loading": "Chargement…",
         "placeholder": "https://url-du-flux",
         "play": "Lire",
+        "processing": "Traitement en cours…",
         "title": "Ajouter un flux"
       }
     },

web-src/src/i18n/zh-CN.json

@@ -36,6 +36,7 @@
         "loading": "加载中…",
         "placeholder": "https://url-to-stream",
         "play": "播放",
+        "processing": "处理中…",
         "title": "添加流"
       }
     },

web-src/src/i18n/zh-TW.json

@@ -36,6 +36,7 @@
         "loading": "載入中…",
         "placeholder": "https://url-to-stream",
         "play": "播放",
+        "processing": "處理中…",
         "title": "新增串流"
       }
     },