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/reporting.py

@@ -0,0 +1,46 @@
+"""Build a tabular overview of all answers for a Form."""
+
+from dataclasses import dataclass
+
+from formbuilder.models import Field
+
+CHOICE_TYPES = {Field.FieldType.CHOICE, Field.FieldType.MULTICHOICE, Field.FieldType.CHECKBOX}
+
+
+@dataclass
+class ReportRow:
+    submission: object
+    values: dict  # field id -> answer value
+
+
+@dataclass
+class FormReport:
+    form: object
+    columns: list  # Field instances, in display order
+    rows: list  # ReportRow, newest submission first
+    summaries: dict  # field id -> {stringified value: count} for choice-like fields
+    count: int
+
+
+def form_report(form):
+    """Return a FormReport: one column per field, one row per submission."""
+    columns = list(form.fields.order_by("order"))
+    summaries = {column.id: {} for column in columns if column.field_type in CHOICE_TYPES}
+
+    rows = []
+    submissions = form.submissions.select_related("member").prefetch_related("answers")
+    for submission in submissions:
+        values = {answer.field_id: answer.value for answer in submission.answers.all()}
+        rows.append(ReportRow(submission=submission, values=values))
+        for field_id, bucket in summaries.items():
+            if field_id in values:
+                _tally(bucket, values[field_id])
+
+    return FormReport(form=form, columns=columns, rows=rows, summaries=summaries, count=len(rows))
+
+
+def _tally(bucket, value):
+    items = value if isinstance(value, list) else [value]
+    for item in items:
+        key = str(item)
+        bucket[key] = bucket.get(key, 0) + 1