feat(formbuilder): fix tenancy bugs, add admin + services

Fix multi-tenancy/integrity bugs in the models: Form.slug and Field.key
were globally unique (unique=True), so two clubs couldn't reuse a form
slug and two forms couldn't reuse a field key — make slug unique per club
(constraint already present) and key unique per form. Add a
(submission, field) uniqueness constraint on Answer.

Register all four models in the admin (Field inline on Form, Answer inline
on Submission) and add formbuilder to the admin registration smoke test.

Add a service layer:
- submit_form(form, member, data): enforces is_active / login_required /
  open window / max_submissions, validates required + choice fields, and
  writes a Submission with Answers atomically (FormSubmissionError carries
  per-field errors).
- build_form(form): a live django.forms.Form built from a Form's active
  fields, mapping each FieldType to the matching form field.
- form_report(form): a tabular overview of every submission's answers plus
  per-value tallies for choice-type fields.

Full suite at 100% coverage.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

formbuilder/services/form_factory.py

@@ -0,0 +1,35 @@
+"""Build a live ``django.forms.Form`` class from a Form instance's fields."""
+
+from django import forms
+
+from formbuilder.models import Field
+
+from .options import field_choices
+
+FIELD_BUILDERS = {
+    Field.FieldType.TEXT: lambda field, kw: forms.CharField(**kw),
+    Field.FieldType.TEXTAREA: lambda field, kw: forms.CharField(widget=forms.Textarea, **kw),
+    Field.FieldType.NUMBER: lambda field, kw: forms.DecimalField(**kw),
+    Field.FieldType.EMAIL: lambda field, kw: forms.EmailField(**kw),
+    Field.FieldType.DATE: lambda field, kw: forms.DateField(**kw),
+    Field.FieldType.CHOICE: lambda field, kw: forms.ChoiceField(choices=field_choices(field), **kw),
+    Field.FieldType.MULTICHOICE: lambda field, kw: forms.MultipleChoiceField(choices=field_choices(field), **kw),
+    Field.FieldType.CHECKBOX: lambda field, kw: forms.BooleanField(**kw),
+    Field.FieldType.FILE: lambda field, kw: forms.FileField(**kw),
+}
+
+
+def _build_field(field):
+    kwargs = {"required": field.required, "label": field.label, "help_text": field.help_text}
+    return FIELD_BUILDERS[field.field_type](field, kwargs)
+
+
+def build_form_class(form):
+    """Return a ``forms.Form`` subclass with a field per active Field, keyed by ``key``."""
+    fields = {field.key: _build_field(field) for field in form.fields.filter(is_active=True).order_by("order")}
+    return type("DynamicForm", (forms.Form,), fields)
+
+
+def build_form(form, data=None, files=None):
+    """Instantiate the dynamic form, bound to ``data``/``files`` when provided."""
+    return build_form_class(form)(data=data, files=files)