feat(championship): surface teammate H2H bars on drivers view (#23)

Add reusable TeammateH2H component and teammatePairs helper that ranks
intra-team battles by closeness, using existing hub teammate_wins data.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/src/test/TeammateH2H.test.tsx

@@ -0,0 +1,54 @@
+import { describe, expect, it } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import { TeammateH2H } from '../components/TeammateH2H'
+
+describe('TeammateH2H', () => {
+  it('renders score and TLAs', () => {
+    render(
+      <TeammateH2H
+        teamName="Red Bull"
+        teamColour="3671c6"
+        driverATla="VER"
+        driverBTla="PER"
+        winsA={9}
+        winsB={1}
+      />,
+    )
+    expect(screen.getByText('VER')).toBeInTheDocument()
+    expect(screen.getByText('PER')).toBeInTheDocument()
+    expect(screen.getByTestId('h2h-score')).toHaveTextContent('9–1')
+    expect(screen.getByText('Red Bull')).toBeInTheDocument()
+  })
+
+  it('sets proportional bar segment widths from wins', () => {
+    render(
+      <TeammateH2H
+        teamName="McLaren"
+        teamColour="ff8000"
+        driverATla="NOR"
+        driverBTla="PIA"
+        winsA={6}
+        winsB={4}
+      />,
+    )
+    const barA = screen.getByTestId('h2h-bar-a')
+    const barB = screen.getByTestId('h2h-bar-b')
+    expect(barA).toHaveStyle({ width: '60%' })
+    expect(barB).toHaveStyle({ width: '40%' })
+  })
+
+  it('shows extra driver note when provided', () => {
+    render(
+      <TeammateH2H
+        teamName="Red Bull"
+        teamColour="3671c6"
+        driverATla="VER"
+        driverBTla="PER"
+        winsA={5}
+        winsB={3}
+        extraNote="+1"
+      />,
+    )
+    expect(screen.getByText('+1')).toBeInTheDocument()
+  })
+})