feat: add Text node type to canvas

New canvas object Text with edit/create modal: text content (single
or multi-line), font (Inter, JetBrains Mono, Serif, System Sans),
size, color, border (style + width + color), background. Double-click
on node opens edit modal. Sidebar gets "Add Text" entry below "Add Zone".

Refs #124

frontend/src/components/modals/__tests__/TextModal.test.tsx

@@ -0,0 +1,75 @@
+import { describe, it, expect, vi } from 'vitest'
+import { render, screen, fireEvent } from '@testing-library/react'
+import { TextModal, type TextFormData } from '../TextModal'
+
+describe('TextModal', () => {
+  it('renders nothing when closed', () => {
+    const { container } = render(
+      <TextModal open={false} onClose={vi.fn()} onSubmit={vi.fn()} />
+    )
+    expect(container.querySelector('[role="dialog"]')).toBeNull()
+  })
+
+  it('renders form fields when open', () => {
+    render(<TextModal open onClose={vi.fn()} onSubmit={vi.fn()} />)
+    expect(screen.getByPlaceholderText('Type text…')).toBeDefined()
+    expect(screen.getByText('Add Text')).toBeDefined()
+    expect(screen.getByText('Police')).toBeDefined()
+    expect(screen.getByText('Border Style')).toBeDefined()
+    expect(screen.getByText('Size')).toBeDefined()
+  })
+
+  it('renders Edit Text title when provided', () => {
+    render(<TextModal open onClose={vi.fn()} onSubmit={vi.fn()} title="Edit Text" />)
+    expect(screen.getByText('Edit Text')).toBeDefined()
+  })
+
+  it('calls onSubmit with form data on submit', () => {
+    const onSubmit = vi.fn()
+    render(<TextModal open onClose={vi.fn()} onSubmit={onSubmit} />)
+    const ta = screen.getByPlaceholderText('Type text…')
+    fireEvent.change(ta, { target: { value: 'Hello' } })
+    fireEvent.click(screen.getByText('Add'))
+    expect(onSubmit).toHaveBeenCalledOnce()
+    const submitted = onSubmit.mock.calls[0][0] as TextFormData
+    expect(submitted.text).toBe('Hello')
+    expect(submitted.font).toBe('inter')
+    expect(submitted.border_style).toBe('none')
+  })
+
+  it('hides Border Width when style is none, shows when not', () => {
+    render(<TextModal open onClose={vi.fn()} onSubmit={vi.fn()} />)
+    expect(screen.queryByText('Border Width')).toBeNull()
+    fireEvent.click(screen.getByTitle('Solid'))
+    expect(screen.getByText('Border Width')).toBeDefined()
+  })
+
+  it('shows Delete button and calls handlers when provided', () => {
+    const onDelete = vi.fn()
+    const onClose = vi.fn()
+    render(<TextModal open onClose={onClose} onSubmit={vi.fn()} onDelete={onDelete} />)
+    fireEvent.click(screen.getByText('Delete'))
+    expect(onDelete).toHaveBeenCalledOnce()
+    expect(onClose).toHaveBeenCalledOnce()
+  })
+
+  it('pre-fills from initial prop', () => {
+    render(
+      <TextModal
+        open
+        onClose={vi.fn()}
+        onSubmit={vi.fn()}
+        initial={{ text: 'Pre-filled', text_size: 24, font: 'mono' }}
+      />
+    )
+    const ta = screen.getByPlaceholderText('Type text…') as HTMLTextAreaElement
+    expect(ta.value).toBe('Pre-filled')
+  })
+
+  it('cancel calls onClose', () => {
+    const onClose = vi.fn()
+    render(<TextModal open onClose={onClose} onSubmit={vi.fn()} />)
+    fireEvent.click(screen.getByText('Cancel'))
+    expect(onClose).toHaveBeenCalledOnce()
+  })
+})