Add input_class and control_class props to form components

[fsecada01]

Closes #1

Summary

• CfFormField, CfSelect, CfTextarea now accept input_class — appended to the main input element's class string alongside Bulma's own classes
• CfCheckboxGroup accepts control_class — appended to the <div class="control"> wrapper
• Both Jinja2/JinjaX and django-cotton template sets updated
• All new props default to "" — no visual change when omitted

Usage

{# Rounded search input #}
<c-cf.form-field name="q" label="Search" value="" error=""
                 type="text" input_class="is-rounded" />

{# Fixed-height textarea #}
<c-cf.textarea name="bio" label="Bio" value="" error=""
               input_class="has-fixed-size" />

{# Flex-wrapped checkbox group #}
<c-cf.checkbox-group name="tags" label="Tags"
                     choices="..." selected="[]" error=""
                     control_class="is-flex is-flex-wrap-wrap gap-2" />

JinjaX equivalent uses the same prop names:

<CfFormField name="q" label="Search" value="" error="" input_class="is-rounded" />

Test Plan

• Jinja2: 8 new tests — prop applied to correct element (FormField, Select, Textarea, CheckboxGroup), default renders without extra class for each
• Cotton: 5 new tests — same coverage for Cotton template set
• All 12 existing form unit tests updated to pass new input_class=""/control_class="" defaults (required by StrictUndefined in the Jinja2 test environment)
• Full suite (114 tests, excluding E2E): all pass
• ruff check and ruff format --check: clean

🤖 Generated with Claude Code