docs: add v0.41.0 changelog entry

HISTORY.md

@@ -1,4 +1,20 @@
 # Bill Tracker — Changelog
+## v0.41.0
+
+### ✨ Spending
+
+- **Category groups** — Organize spending categories into named groups (e.g. "Bills", "Everyday", "Subscriptions"). New `category_groups` table with CRUD endpoints. Categories can be assigned to a group via the Spending page or API. Groups appear as collapsible headers in the category breakdown.
+- **YNAB-style spending page** — Complete overhaul: all spending-enabled categories are always visible (even with $0 activity), budget/spent/remaining overview strip, Ready to Assign card, 3-month spending averages per category, progress bars with color-coded levels (ok/warn/over), available/overspent labels.
+- **Cover overspending** — When a category is over budget, a "Cover from…" dropdown shows other categories with available budget. Clicking one reallocates budget between the two categories.
+- **Spending page settings** — Toggle Ready to Assign, 3-month averages, Cover overspending, and Category groups via a dropdown menu. Settings persist per user.
+- **"Other categories" bundle** — Outflows assigned to non-spending-enabled categories are bundled into a single read-only row so totals stay accurate without polluting the spending-enabled list.
+- **Error states** — Summary, transactions, and categories each have their own error state with retry button. Skeleton loading for all sections.
+
+### 🧪 Tests
+
+- `tests/categoryGroups.test.js` — 4 tests: create/list/rename/delete, duplicate name rejection, group ownership validation, category assignment
+- `tests/spendingSummary.test.js` — 4 tests: budgeted category with no activity, non-spending category bundling, 3-month average calculation, category groups in response
+
 ## v0.38.4
 
 ### ✨ Money