Display server validation field errors inline in forms

[Copilot]

When the server returns a VALIDATION_ERROR (HTTP 400), the UI now shows per-field error messages in the third column of the form table (red, bold) in addition to the existing status-area message.

Changes

browser2/js/src/markup.js

• crud.create / crud.update: Extract field_errors from VALIDATION_ERROR responses; always include field_errors: {} in all return objects (clears errors on success/network error)
• createFormElement: After rendering each field row, append a span.field-error with the field's error message if currentState.field_errors[fieldKey] is set

browser2/js/src/style.css

• Added .field-error { color: red; font-weight: bold; }

Page spec state defaults

• builtin-mapp-model.json → create_model_state: added field_errors: {}
• builtin-mapp-model-instance.json → model_instance: added field_errors: {}

Both are required so the lingo state type system accepts field_errors as a valid struct field when CRUD responses set it. Field errors are cleared automatically on successful create/update.

Tests (templates/mapp-py/tests/crud.spec.js, templates/sosh-net/tests/crud.spec.js)

Added test validation errors are displayed in form: mocks a VALIDATION_ERROR POST response with field_errors, submits the form, and asserts both the status message and .field-error span are visible with the correct content.

Example response handled

{
  "error": {
    "code": "VALIDATION_ERROR",
    "message": "This model has failed validation",
    "field_errors": {
      "x_bool": "Must be a boolean value",
      "x_int": "Must be an integer"
    }
  }
}

Each key in field_errors maps to its form row's third column; fields without an entry show their description as before.