Guard against non-object JSON when switching to table mode in EnvironmentForm

[Copilot]

When switching extra-vars to table mode, JSON.parse output was passed directly to Object.keys() without verifying it was a plain object. Scalars, null, and arrays all satisfy Object.keys() — producing rows with numeric/character keys — so saving would silently reshape the stored JSON into an object with a different structure.

Changes

• web/src/components/EnvironmentForm.vue — extraVarsEditMode watcher, case 'table': added a type guard after JSON.parse that falls back to JSON mode if the parsed value is not a plain object:

if (extraVars === null || typeof extraVars !== 'object' || Array.isArray(extraVars)) {
  this.extraVarsEditMode = 'json';
  return;
}

Arrays ([]), strings ("abc"), numbers, and null at the root level now keep the editor in JSON mode instead of being silently converted to object-shaped rows on save.