fix(service): block UI editing of file volumes exceeding 5 MiB

Large host files mounted via Docker volumes caused the storages page to
become unusable — full file content was stored in the encrypted mediumText
column and serialised into the Livewire payload, crashing the browser.

- Add MAX_CONTENT_SIZE (5 MiB), BINARY_PLACEHOLDER, and TOO_LARGE_PLACEHOLDER
  constants to LocalFileVolume
- Check remote file size via stat/wc before cat in loadStorageOnServer and
  saveStorageOnServer; store placeholder instead of content when limit exceeded
- Expose is_too_large computed attribute (appended for Livewire serialisation)
- Guard submit, instantSave, and syncData in FileStorage Livewire component
- Truncate oversized content in Storage::refreshStorages to prevent payload bloat
- Show distinct warning banner in file-storage blade; mark textarea readonly and
  hide Save/Convert buttons for too-large files
- Add unit tests covering constants, computed flags, and toArray serialisation

Fixes #4701

app/Livewire/Project/Service/Storage.php

@@ -69,7 +69,11 @@ class Storage extends Component
 
     public function refreshStorages()
     {
-        $this->fileStorage = $this->resource->fileStorages()->get();
+        $this->fileStorage = $this->resource->fileStorages()->get()->each(function (LocalFileVolume $fs) {
+            if (strlen((string) $fs->content) > LocalFileVolume::MAX_CONTENT_SIZE) {
+                $fs->content = LocalFileVolume::TOO_LARGE_PLACEHOLDER;
+            }
+        });
         $this->resource->load('persistentStorages.resource');
     }