fix(downloads): a conversion's commit, a stopped upload, the fast join and a clip's copy hold up

- The fast join gives each ffconcat entry its own media-only format whitelist, so a library file
  can no longer be opened as a nested concat list (the list's whitelist was handed down to it).
- A file the guarded probe cannot read is a download-only file, not a guess from yt-dlp's info.
- A conversion's or an ingest's commit that raises is re-read in a fresh session before any file
  is removed: a commit that landed keeps the file its row now names.
- An original that cannot be removed after conversion is logged; the upload stays ready.
- An upload whose conversion is cancelled or deleted midway is freed once nothing holds it; a
  paused one is kept.
- A shared link says "preparing" only while its video's job is queued or running.
- The admin storage view counts every file on disk ("Files on disk"), not only ready ones.
- A clip's failure title, unknown failure and cancel dialog, and a clip's and an upload's delete
  dialog speak of what the job made; an upload's quota refusal explains that the original is kept.
- /watch announces "preparing" as an alert and moves focus to the new Retry after an action.

frontend/src/i18n/locales/en/downloads.json

@@ -155,8 +155,15 @@
     "cancelUploadTitle": "Delete upload?",
     "cancelUploadBody": "The file you uploaded is removed from the server along with it.",
     "cancelUploadAction": "Delete upload",
+    "cancelEditTitle": "Cancel clip?",
+    "cancelEditBody": "This stops making the clip and removes it from your queue.",
+    "cancelEditAction": "Stop making this clip",
     "deleteTitle": "Delete download?",
     "deleteBody": "This deletes it from your downloads. The file may stay cached for other users until it expires.",
+    "deleteUploadTitle": "Delete upload?",
+    "deleteUploadBody": "The uploaded file is removed from the server. This can't be undone.",
+    "deleteEditTitle": "Delete clip?",
+    "deleteEditBody": "The clip is removed from the server. This can't be undone.",
     "removeSharedTitle": "Remove from your list?",
     "removeSharedBody": "This removes it from your shared list only — it won't delete the owner's file.",
     "redownloadTitle": "Re-download this file?",
@@ -187,7 +194,7 @@
     "deleteConfirm": "Delete the format “{{name}}”?"
   },
   "admin": {
-    "readyFiles": "Ready files",
+    "filesOnDisk": "Files on disk",
     "totalSize": "Total size",
     "cap": "Cache cap",
     "noCap": "no cap",
@@ -231,8 +238,20 @@
     "fail": {
       "title": "Couldn't download",
       "titleUpload": "The upload isn't ready",
+      "titleEdit": "The clip isn't ready",
       "detailsLink": "details",
       "detailsToggle": "Technical details",
+      "upload": {
+        "quota_exceeded": {
+          "body": "The phone-ready version of this upload would not fit in your storage quota. Your original is kept – delete something from your library, then try again."
+        }
+      },
+      "edit": {
+        "unknown": {
+          "short": "Couldn't make the clip",
+          "body": "Something went wrong while making this clip. The technical details below may help."
+        }
+      },
       "cat": {
         "unavailable": {
           "short": "Video unavailable",

frontend/src/i18n/locales/hu/downloads.json

@@ -155,8 +155,15 @@
     "cancelUploadTitle": "Törlöd a feltöltést?",
     "cancelUploadBody": "A feltöltött fájl is törlődik a szerverről.",
     "cancelUploadAction": "Feltöltés törlése",
+    "cancelEditTitle": "Megszakítod a klipet?",
+    "cancelEditBody": "Ez leállítja a klip készítését és eltávolítja a sorból.",
+    "cancelEditAction": "Klip készítésének leállítása",
     "deleteTitle": "Törlöd a letöltést?",
     "deleteBody": "Ez törli a letöltéseid közül. A fájl a lejáratáig még a gyorsítótárban maradhat mások számára.",
+    "deleteUploadTitle": "Törlöd a feltöltést?",
+    "deleteUploadBody": "A feltöltött fájl törlődik a szerverről. Ez nem vonható vissza.",
+    "deleteEditTitle": "Törlöd a klipet?",
+    "deleteEditBody": "A klip törlődik a szerverről. Ez nem vonható vissza.",
     "removeSharedTitle": "Eltávolítod a listádból?",
     "removeSharedBody": "Csak a te megosztott listádból tűnik el — a tulajdonos fájlját nem törli.",
     "redownloadTitle": "Újraletöltöd ezt a fájlt?",
@@ -187,7 +194,7 @@
     "deleteConfirm": "Törlöd a(z) „{{name}}” formátumot?"
   },
   "admin": {
-    "readyFiles": "Kész fájlok",
+    "filesOnDisk": "Fájlok a lemezen",
     "totalSize": "Teljes méret",
     "cap": "Gyorsítótár-korlát",
     "noCap": "nincs korlát",
@@ -231,8 +238,20 @@
     "fail": {
       "title": "Nem sikerült letölteni",
       "titleUpload": "A feltöltés nem készült el",
+      "titleEdit": "A klip nem készült el",
       "detailsLink": "részletek",
       "detailsToggle": "Technikai részletek",
+      "upload": {
+        "quota_exceeded": {
+          "body": "A feltöltés telefonra alakított változata nem fér bele a tárhelykeretedbe. Az eredeti megmaradt – törölj valamit a könyvtáradból, majd próbáld újra."
+        }
+      },
+      "edit": {
+        "unknown": {
+          "short": "Nem sikerült elkészíteni a klipet",
+          "body": "Hiba történt a klip készítése közben. Az alábbi technikai részletek segíthetnek."
+        }
+      },
       "cat": {
         "unavailable": {
           "short": "A videó nem elérhető",