Add department budget % allocation

- Budgets page: new dept split section with % inputs, equal-split button, save
- Weekly/Monthly: per-dept budget column using dept pcts from actuals response
- Backend: dept_budget_pcts in ALLOWED_KEYS; actuals returns dept_pcts map;
  budgets route adds GET /dept-config + PUT /dept-pcts endpoints

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/types.ts

@@ -47,3 +47,9 @@ export interface AppSetting {
   value: string
   updated_at: string
 }
+
+export interface DeptPct {
+  id: string
+  name: string
+  pct: number
+}