test(03-00): add Wave 0 test stub files for 4 components

- BudgetSetup.test.tsx: smoke test + 2 it.skip for IXTN-01 spinner/disable
- CategoriesPage.test.tsx: smoke test + 4 it.skip for IXTN-05 and STATE-02
- DashboardPage.test.tsx: smoke test + 2 it.skip for STATE-01 and STATE-03
- BillsTracker.test.tsx: smoke test + 3 it.skip for STATE-03 and IXTN-03

frontend/src/components/BillsTracker.test.tsx

@@ -0,0 +1,54 @@
+import { render, screen } from '@testing-library/react'
+import { describe, it, expect, vi } from 'vitest'
+import { BillsTracker } from './BillsTracker'
+import type { BudgetDetail } from '@/lib/api'
+
+vi.mock('react-i18next', () => ({
+  useTranslation: () => ({ t: (key: string) => key, i18n: { language: 'en' } }),
+}))
+
+const emptyBudgetFixture: BudgetDetail = {
+  id: 'b1',
+  name: 'Test Budget',
+  start_date: '2025-01-01',
+  end_date: '2025-01-31',
+  currency: 'EUR',
+  carryover_amount: 0,
+  items: [],
+  totals: {
+    income_budget: 0,
+    income_actual: 0,
+    bills_budget: 0,
+    bills_actual: 0,
+    expenses_budget: 0,
+    expenses_actual: 0,
+    debts_budget: 0,
+    debts_actual: 0,
+    savings_budget: 0,
+    savings_actual: 0,
+    investments_budget: 0,
+    investments_actual: 0,
+    available: 0,
+  },
+}
+
+describe('BillsTracker', () => {
+  it('renders without crashing', () => {
+    render(<BillsTracker budget={emptyBudgetFixture} onUpdate={vi.fn()} />)
+    expect(screen.getByText('dashboard.billsTracker')).toBeInTheDocument()
+  })
+
+  it.skip('shows tinted skeleton when no bill items', () => {
+    // STATE-03: when budget.items contains no bill-type items, BillsTracker renders
+    // skeleton rows with a bill-category tint (palette bill light shade) instead of an empty table body
+  })
+
+  it.skip('flashes row green on successful inline save', () => {
+    // IXTN-03: after onUpdate resolves successfully, the updated row briefly gets a green
+    // flash class before returning to its normal appearance
+  })
+
+  it.skip('flashes row red on failed inline save', () => {
+    // IXTN-03: after onUpdate rejects, the row briefly gets a red flash class to signal failure
+  })
+})

frontend/src/components/BudgetSetup.test.tsx

@@ -0,0 +1,37 @@
+import { render, screen } from '@testing-library/react'
+import { describe, it, expect, vi } from 'vitest'
+import { BudgetSetup } from './BudgetSetup'
+
+vi.mock('react-i18next', () => ({
+  useTranslation: () => ({ t: (key: string) => key, i18n: { language: 'en' } }),
+}))
+
+vi.mock('@/lib/api', () => ({
+  budgets: {
+    create: vi.fn().mockResolvedValue({ id: 'b1', name: 'Test Budget' }),
+    copyFrom: vi.fn().mockResolvedValue({}),
+  },
+}))
+
+describe('BudgetSetup', () => {
+  const defaultProps = {
+    existingBudgets: [],
+    onCreated: vi.fn(),
+    onCancel: vi.fn(),
+  }
+
+  it('renders without crashing', () => {
+    render(<BudgetSetup {...defaultProps} />)
+    expect(screen.getByText('budget.setup')).toBeInTheDocument()
+  })
+
+  it.skip('shows spinner in create button when saving', () => {
+    // IXTN-01: while saving is true, the create button renders a spinner (Loader2 icon)
+    // Steps: fill required fields, click create, assert spinner is visible before resolve
+  })
+
+  it.skip('disables create button when saving', () => {
+    // IXTN-01: while saving is true, the create button is disabled to prevent double-submit
+    // Steps: fill required fields, click create, assert button is disabled before resolve
+  })
+})