fix(sidebar): verify folder deletion against the backend

The sidebar derives "empty folder" from the models-only list, which omits
models flagged `exclude: true`, while the delete guard walks the folder on
disk and refuses on any weight file. A folder whose models are all excluded
therefore looked empty, offered the confirmation, and then failed with
"still contains models".

The delete modal still opens on that prediction, but is now corrected by a
dry run of the very delete the user is about to confirm, so the button state
cannot contradict the backend. The confirm button stays disabled while the
check runs, and a late answer is discarded once the modal is dismissed or
retargeted. The dry run also covers weight files no scanner indexes (a lora
folder holding only a `.gguf`, say) and files that appeared after the last
scan.

`_collect_folder_manifest()` now reports `excluded_model_count`, and the
refusal names the excluded models, so the message explains the mismatch
instead of reading like a bug. Locale files carry the sync placeholders in
this commit; the translations follow.

locales/he.json

@@ -1350,6 +1350,10 @@
             "emptyNote": "אין מודלים בתיקייה זו. קבצים אחרים שבה יימחקו גם הם.",
             "notEmptyTitle": "התיקייה אינה ריקה",
             "notEmptyMessage": "בתיקייה זו עדיין יש מודלים. מחק או העבר אותם תחילה — מחיקת תיקייה לעולם אינה מוחקת קובצי מודלים.",
+            "notEmptyMessageCount": "[TODO: Translate] This folder still contains {count} model file(s). Delete or move them first — deleting a folder never cascades over model files.",
+            "notEmptyMessageExcluded": "[TODO: Translate] This folder still contains {count} model file(s), {excluded} of them excluded from the library. Un-exclude them in Manage Excluded Models and delete them first — deleting a folder never cascades over model files.",
+            "busyTitle": "[TODO: Translate] A deletion is still pending",
+            "checking": "[TODO: Translate] Checking the folder contents...",
             "confirm": "מחק תיקייה"
         },
         "deleteFolderResult": {
@@ -1358,6 +1362,7 @@
             "restored": "התיקייה שוחזרה",
             "failed": "מחיקת התיקייה נכשלה: {message}",
             "notEmpty": "בתיקייה זו עדיין יש מודלים. רענן את סרגל הצד ונסה שוב.",
+            "notEmptyWithCount": "[TODO: Translate] This folder still contains {count} model file(s). Refresh the sidebar and try again.",
             "busy": "מחיקה עדיין ממתינה בתיקייה זו. המתן לסיום חלון הביטול.",
             "unsupported": "מחיקת תיקיות אינה נתמכת בדף זה",
             "noRoot": "לא הוגדר שורש מודלים"