fix(files): address autosave migration and review regressions

Seed omitted autoSaveEnabled from the hydrated client preference (including
legacy localStorage) instead of resetting everyone to enabled. Restore SVG
non-editable flags, treat clean draft saves as success, and throw again from
disposed content-cache owners while keeping runtime-switch cache invalidation.

Co-authored-by: Serhii Dziupin <makeittech@users.noreply.github.com>

packages/ui/src/lib/fileEditorAutosave.ts

@@ -38,12 +38,18 @@ export type FileEditorSaveDraftGate = {
 };
 
 /**
- * Whether saveDraft may write. Refuses empty drafts against stale content and any binary target.
+ * Whether saveDraft may proceed.
+ * - Clean drafts return true ("nothing to save" is success) so callers like the
+ *   unsaved-changes dialog and Ctrl+S do not treat a no-op as failure.
+ * - Incomplete loads and binary targets return false (refused).
  */
 export function shouldAllowFileDraftSave(gate: FileEditorSaveDraftGate): boolean {
-  if (!gate.selectedFilePath || !gate.isDirty) {
+  if (!gate.selectedFilePath) {
     return false;
   }
+  if (!gate.isDirty) {
+    return true;
+  }
   if (gate.fileLoading || gate.loadedFilePath !== gate.selectedFilePath || gate.isNonEditableBinary) {
     return false;
   }