feat: add CRM lead assignment strategies

supabase/migrations/202606290026_crm_lead_assignment.sql

@@ -0,0 +1,30 @@
+alter table public.crm_config
+  add column if not exists assignment_mode text not null default 'none',
+  add column if not exists assignment_pool jsonb not null default '[]'::jsonb,
+  add column if not exists assignment_cursor integer not null default 0,
+  add column if not exists assignment_config jsonb not null default '{}'::jsonb;
+
+do $$
+begin
+  if not exists (
+    select 1
+    from pg_constraint
+    where conname = 'crm_config_assignment_mode_check'
+  ) then
+    alter table public.crm_config
+      add constraint crm_config_assignment_mode_check
+      check (assignment_mode in ('none', 'direct', 'round_robin', 'referrer'));
+  end if;
+end $$;
+
+alter table public.referral_leads
+  add column if not exists assigned_to_user_id uuid references public.platform_users(id) on delete set null,
+  add column if not exists assignment_mode text,
+  add column if not exists assigned_at timestamptz,
+  add column if not exists assigned_by uuid references public.platform_users(id) on delete set null;
+
+create index if not exists idx_referral_leads_assignee
+  on public.referral_leads(tenant_id, assigned_to_user_id, status, bound_at desc);
+
+create index if not exists idx_crm_config_assignment_mode
+  on public.crm_config(tenant_id, assignment_mode);