feat(settings): directory picker and live validation for path settings

Add a reusable directory-picker modal backed by a new generic
POST /api/lm/browse-directory endpoint (browse logic extracted from the
recipe batch-import handler into py/utils/directory_browser.py) and wire
a browse button plus advisory validate-path feedback (POST
/api/lm/validate-path) into the settings path inputs: recipes path,
example images path/local root, and the extra-folder/model-path rows.

The browse button insets into the right edge of static inputs so narrow
settings rows keep their single-control layout.

Translations for the new settings.directoryPicker and
settings.pathValidation keys are filled in for all 9 locales.

locales/he.json

@@ -608,6 +608,22 @@
                 "controlnet": "נתיבי ControlNet"
             }
         },
+        "directoryPicker": {
+            "title": "עיון בתיקיות",
+            "selectFolder": "בחר תיקייה זו",
+            "goUp": "למעלה",
+            "pathPlaceholder": "הזן נתיב...",
+            "go": "עבור",
+            "emptyFolder": "אין תתי-תיקיות",
+            "loadError": "טעינת התיקייה נכשלה"
+        },
+        "pathValidation": {
+            "valid": "הנתיב תקין",
+            "pathNotFound": "הנתיב לא קיים",
+            "notADirectory": "לא תיקייה",
+            "notReadable": "הנתיב לא ניתן לקריאה",
+            "notWritable": "הנתיב לא ניתן לכתיבה"
+        },
         "priorityTags": {
             "title": "תגיות עדיפות",
             "description": "התאם את סדר העדיפות של התגיות עבור כל סוג מודל (לדוגמה: character, concept, style(toon|toon_style))",