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/components/TeammateH2H.tsx

@@ -0,0 +1,55 @@
+import { teamColor } from '../utils'
+import '../styles/h2h.css'
+
+export interface TeammateH2HProps {
+  teamName: string
+  teamColour: string
+  driverATla: string
+  driverBTla: string
+  winsA: number
+  winsB: number
+  /** e.g. "+1" when more than two drivers share the team. */
+  extraNote?: string
+}
+
+export function TeammateH2H({
+  teamName,
+  teamColour,
+  driverATla,
+  driverBTla,
+  winsA,
+  winsB,
+  extraNote,
+}: TeammateH2HProps) {
+  const total = winsA + winsB || 1
+  const pctA = (winsA / total) * 100
+  const color = teamColor(teamColour)
+
+  return (
+    <div className="h2h-row" data-testid="teammate-h2h">
+      <div className="h2h-team">
+        <span className="h2h-team-name">{teamName}</span>
+        {extraNote ? <span className="h2h-extra mono">{extraNote}</span> : null}
+      </div>
+      <div className="h2h-bar-wrap">
+        <span className="h2h-tla h2h-tla--left mono">{driverATla}</span>
+        <div className="h2h-bar" data-testid="h2h-bar">
+          <span
+            className="h2h-bar-seg"
+            data-testid="h2h-bar-a"
+            style={{ width: `${pctA}%`, background: color }}
+          />
+          <span
+            className="h2h-bar-seg h2h-bar-seg--muted"
+            data-testid="h2h-bar-b"
+            style={{ width: `${100 - pctA}%`, background: color }}
+          />
+          <span className="h2h-score mono" data-testid="h2h-score">
+            {winsA}–{winsB}
+          </span>
+        </div>
+        <span className="h2h-tla h2h-tla--right mono">{driverBTla}</span>
+      </div>
+    </div>
+  )
+}