feat: add platform invoice dunning workflow

supabase/migrations/202606300001_platform_invoice_dunning.sql

@@ -0,0 +1,41 @@
+create table if not exists public.tenant_invoice_reminders (
+  id uuid primary key default gen_random_uuid(),
+  tenant_id uuid not null references public.tenants(id) on delete cascade,
+  invoice_id uuid not null references public.tenant_invoices(id) on delete cascade,
+  reminder_type text not null default 'overdue' check (reminder_type in ('due_soon', 'overdue', 'final_notice', 'manual')),
+  channel text not null default 'manual' check (channel in ('manual', 'internal', 'sms', 'email', 'wechat', 'crm')),
+  status text not null default 'pending' check (status in ('pending', 'sent', 'acknowledged', 'dismissed', 'failed')),
+  reminder_date date not null default current_date,
+  reminder_level integer not null default 1,
+  due_date date,
+  balance_cents_snapshot integer not null default 0,
+  message text,
+  metadata jsonb not null default '{}'::jsonb,
+  created_by uuid references public.platform_users(id) on delete set null,
+  sent_at timestamptz,
+  acknowledged_at timestamptz,
+  created_at timestamptz not null default now(),
+  updated_at timestamptz not null default now()
+);
+
+create unique index if not exists uniq_tenant_invoice_reminders_daily
+  on public.tenant_invoice_reminders(tenant_id, invoice_id, reminder_type, channel, reminder_date);
+
+create index if not exists idx_tenant_invoice_reminders_tenant_status
+  on public.tenant_invoice_reminders(tenant_id, status, reminder_date desc);
+
+create index if not exists idx_tenant_invoice_reminders_invoice
+  on public.tenant_invoice_reminders(invoice_id, reminder_date desc);
+
+alter table public.tenant_invoice_reminders enable row level security;
+
+drop policy if exists tenant_isolation on public.tenant_invoice_reminders;
+create policy tenant_isolation on public.tenant_invoice_reminders
+  for all
+  using (tenant_id = app.current_tenant_id() or app.is_platform_admin())
+  with check (tenant_id = app.current_tenant_id() or app.is_platform_admin());
+
+drop trigger if exists set_updated_at on public.tenant_invoice_reminders;
+create trigger set_updated_at
+  before update on public.tenant_invoice_reminders
+  for each row execute function app.touch_updated_at();