test: add folder tree and filtering tests; docs: ADR-0033

Add FolderTree component tests (render, expand, collapse, select,
highlight) and folder filtering tests in noteListHelpers (path
matching, sibling exclusion, archive/trash filtering).

ADR-0033 documents the decision to scan all subdirectories and
expose folder tree navigation, superseding ADR-0006's scanning
constraint.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/components/FolderTree.test.tsx

@@ -0,0 +1,70 @@
+import { render, screen, fireEvent } from '@testing-library/react'
+import { describe, it, expect, vi } from 'vitest'
+import { FolderTree } from './FolderTree'
+import type { FolderNode, SidebarSelection } from '../types'
+
+const mockFolders: FolderNode[] = [
+  {
+    name: 'projects',
+    path: 'projects',
+    children: [
+      { name: 'laputa', path: 'projects/laputa', children: [] },
+      { name: 'portfolio', path: 'projects/portfolio', children: [] },
+    ],
+  },
+  { name: 'areas', path: 'areas', children: [] },
+  { name: 'journal', path: 'journal', children: [] },
+]
+
+const defaultSelection: SidebarSelection = { kind: 'filter', filter: 'all' }
+
+describe('FolderTree', () => {
+  it('renders nothing when folders is empty', () => {
+    const { container } = render(
+      <FolderTree folders={[]} selection={defaultSelection} onSelect={vi.fn()} />,
+    )
+    expect(container.firstChild).toBeNull()
+  })
+
+  it('renders FOLDERS header and top-level folders', () => {
+    render(<FolderTree folders={mockFolders} selection={defaultSelection} onSelect={vi.fn()} />)
+    expect(screen.getByText('FOLDERS')).toBeInTheDocument()
+    expect(screen.getByText('projects')).toBeInTheDocument()
+    expect(screen.getByText('areas')).toBeInTheDocument()
+    expect(screen.getByText('journal')).toBeInTheDocument()
+  })
+
+  it('does not show children initially', () => {
+    render(<FolderTree folders={mockFolders} selection={defaultSelection} onSelect={vi.fn()} />)
+    expect(screen.queryByText('laputa')).not.toBeInTheDocument()
+  })
+
+  it('calls onSelect with folder kind when clicking a folder', () => {
+    const onSelect = vi.fn()
+    render(<FolderTree folders={mockFolders} selection={defaultSelection} onSelect={onSelect} />)
+    fireEvent.click(screen.getByText('projects'))
+    expect(onSelect).toHaveBeenCalledWith({ kind: 'folder', path: 'projects' })
+  })
+
+  it('expands children when clicking a folder with children', () => {
+    const onSelect = vi.fn()
+    render(<FolderTree folders={mockFolders} selection={defaultSelection} onSelect={onSelect} />)
+    fireEvent.click(screen.getByText('projects'))
+    expect(screen.getByText('laputa')).toBeInTheDocument()
+    expect(screen.getByText('portfolio')).toBeInTheDocument()
+  })
+
+  it('collapses section when clicking FOLDERS header', () => {
+    render(<FolderTree folders={mockFolders} selection={defaultSelection} onSelect={vi.fn()} />)
+    expect(screen.getByText('projects')).toBeInTheDocument()
+    fireEvent.click(screen.getByText('FOLDERS'))
+    expect(screen.queryByText('projects')).not.toBeInTheDocument()
+  })
+
+  it('highlights selected folder', () => {
+    const sel: SidebarSelection = { kind: 'folder', path: 'areas' }
+    render(<FolderTree folders={mockFolders} selection={sel} onSelect={vi.fn()} />)
+    const btn = screen.getByText('areas').closest('button')!
+    expect(btn.className).toContain('text-primary')
+  })
+})