fix(frontend): double-escape Python newline strings in toolFsEdit and finalize doubled-path fixes

vibn-frontend/app/api/mcp/route.ts

@@ -5044,16 +5044,16 @@ except FileNotFoundError:
 new_str = spec['newString']
 
 if spec['hasLineNumbers']:
-  lines = src.split('\n')
+  lines = src.split('\\n')
   start = max(0, spec['startLine'] - 1)
   end = min(len(lines), spec['endLine'])
   if start > len(lines):
     sys.stderr.write('startLine is past end of file'); sys.exit(2)
-  new_lines = new_str.split('\n')
+  new_lines = new_str.split('\\n')
   if len(new_lines) > 1 and new_lines[-1] == '':
     new_lines = new_lines[:-1]
   lines[start:end] = new_lines
-  out = '\n'.join(lines)
+  out = '\\n'.join(lines)
   n = 1
 else:
   old = spec['oldString']