add create signup code

Femto.Database/Migrations/20250518163039_InitSignupCode.sql

@@ -0,0 +1,14 @@
+-- Migration: InitSignupCode
+-- Created at: 18/05/2025 16:30:39
+
+CREATE TABLE authn.signup_code
+(
+    code              varchar(32) PRIMARY KEY,
+    recipient_email   TEXT        NOT NULL,
+    recipient_name    TEXT        NOT NULL,
+    created_at        TIMESTAMPTZ NOT NULL DEFAULT now(),
+    expires_at        TIMESTAMPTZ,
+    -- we don't make this a foreign key as we don't really need it for lookups,
+    -- and should the redeeming user delete be deleted, it's better that we keep the ID here
+    redeeming_user_id UUID
+);