feat: add budget folder schema and migration

scripts/demo-data.ts

@@ -47,6 +47,7 @@ actions.setRuleOverride(d, "2026-09", social.id, { kind: "fixed", amount: { amou
 // every combination at once.
 const wowSub = actions.addRecurringCost(d, {
   name: "World of Warcraft",
+  folderId: null,
   archived: false,
   amount: { amount: 13, currency: "USD" },
   startDate: "2026-06-05",
@@ -57,6 +58,7 @@ const wowSub = actions.addRecurringCost(d, {
 });
 actions.addRecurringCost(d, {
   name: "Rent",
+  folderId: null,
   archived: false,
   amount: { amount: 8200, currency: "DKK" },
   startDate: "2026-06",
@@ -67,6 +69,7 @@ actions.addRecurringCost(d, {
 });
 actions.addRecurringCost(d, {
   name: "Veg box",
+  folderId: null,
   archived: false,
   amount: { amount: 175, currency: "DKK" },
   startDate: "2026-06-06",
@@ -79,6 +82,7 @@ actions.addRecurringCost(d, {
 // off-schedule payment moves the whole series — the phone-bill behaviour.
 actions.addRecurringCost(d, {
   name: "Car insurance",
+  folderId: null,
   archived: false,
   amount: { amount: 349, currency: "DKK" },
   startDate: "2026-08-14",