feat(forms): space-scoped public URL /f/[space]/[slug] (P6)

- migration 028: drop global UNIQUE(forms.slug), add
  UNIQUE(space_id, slug); schema.sql mirrored. Form slugs are now
  unique per space (fixes cross-tenant slug squatting)
- getPublicForm now takes { space, slug }: resolves the space by its
  slug then the form by space_id + slug (maybeSingle)
- route moved app/f/[slug] -> app/f/[space]/[slug]; the public client
  submits by formId (slug is no longer globally unambiguous) and the
  sign-in link round-trips the full /f/space/slug path
- forms-guard returns the space slug; the builder + forms list show
  the full /f/<space>/<slug> share URL; new/edit pass it through
- middleware /f allowlist already covers /f/<space>/<slug>
- getPublicFormSchema + tests updated (333 pass)

build verified (Compiled successfully, exit 0; new route present). No deploy.

app/(app)/forms/[id]/edit/page.tsx

@@ -8,7 +8,7 @@ export const dynamic = 'force-dynamic'
 
 export default async function EditFormPage({ params }: { params: Promise<{ id: string }> }) {
   const { id } = await params
-  const { supabase, member } = await requireFormsManagerPage()
+  const { supabase, member, spaceSlug } = await requireFormsManagerPage()
 
   const { data: form } = await supabase
     .from('forms')
@@ -28,6 +28,7 @@ export default async function EditFormPage({ params }: { params: Promise<{ id: s
         <FormBuilder
           initial={{
             id: form.id,
+            spaceSlug,
             slug: form.slug,
             title: form.title,
             description: form.description ?? '',

app/(app)/forms/forms-client.tsx

@@ -24,7 +24,7 @@ const VIS_LABEL: Record<string, string> = {
   public_anon: 'Public',
 }
 
-export function FormsClient({ forms }: { forms: FormRow[] }) {
+export function FormsClient({ forms, spaceSlug }: { forms: FormRow[]; spaceSlug: string }) {
   return (
     <>
       <PageHeader>
@@ -65,7 +65,7 @@ export function FormsClient({ forms }: { forms: FormRow[] }) {
                     </Link>
                     {f.kind === 'waiver' && <Badge variant="secondary">Waiver</Badge>}
                   </div>
-                  <p className="font-mono text-xs text-muted-foreground">/f/{f.slug}</p>
+                  <p className="font-mono text-xs text-muted-foreground">/f/{spaceSlug}/{f.slug}</p>
                 </div>
                 <Badge variant="outline">{VIS_LABEL[f.visibility] ?? f.visibility}</Badge>
                 <Badge variant={f.status === 'published' ? 'default' : 'secondary'}>

app/(app)/forms/new/page.tsx

@@ -5,7 +5,7 @@ import { FormBuilder } from '@/components/forms/form-builder'
 export const dynamic = 'force-dynamic'
 
 export default async function NewFormPage() {
-  await requireFormsManagerPage()
+  const { spaceSlug } = await requireFormsManagerPage()
 
   return (
     <>
@@ -15,6 +15,7 @@ export default async function NewFormPage() {
       <div className="p-4 md:p-6">
         <FormBuilder
           initial={{
+            spaceSlug,
             slug: '',
             title: '',
             description: '',

app/(app)/forms/page.tsx

@@ -4,7 +4,7 @@ import { FormsClient } from './forms-client'
 export const dynamic = 'force-dynamic'
 
 export default async function FormsPage() {
-  const { supabase, member } = await requireFormsManagerPage()
+  const { supabase, member, spaceSlug } = await requireFormsManagerPage()
 
   const { data: forms } = await supabase
     .from('forms')
@@ -12,5 +12,5 @@ export default async function FormsPage() {
     .eq('space_id', member.space_id)
     .order('created_at', { ascending: false })
 
-  return <FormsClient forms={forms ?? []} />
+  return <FormsClient forms={forms ?? []} spaceSlug={spaceSlug} />
 }