Added YAML object edit and result fields - fixes #1269

[philayres]

Summary

Implements #1269 by adding edit and result-field support for yaml_object_* fields backed by text/string columns.

• Adds a YAML CodeMirror edit field that preserves the submitted YAML text in the backing text/string column.
• Validates submitted YAML as a Hash or Array while leaving JSON/JSONB columns on their existing conversion path.
• Parses stored YAML in the result template and reuses the existing structured/collapsible object renderer.
• Loads, initializes, and synchronizes CodeMirror editors in the main application, covering the existing JSON/JSONB editors as well as YAML-object fields.
• Restricts YAML-object dispatch to compatible text/string columns.
• Skips transformed attributes that are absent from submitted parameters, preventing partial updates from clearing existing YAML or JSON values.
• Extends the system workflow assertions to verify that nested YAML keys and values are actually rendered, not only the object container.

Testing

• bundle exec rspec spec/models/dynamic/field_edit_as/handler_spec.rb - 13 examples, 0 failures.
• app-scripts/headless_rspec.sh spec/system/dynamic_model/dynamic_model_yaml_object_spec.rb - 2 examples, 0 failures.
• Focused model, helper, and view specs previously passed with 36 examples; the handler follow-up adds 3 regression examples.
• Jasmine runs 149 specs with one unchanged pre-existing failure in _fpa_substitution_spec.js.

Fixes #1269.
Part of #1251.