feat: GripAnalysisView — car grip envelope visualization

- New GripAnalysisView with 4 scatter charts:
  1. Grip Envelope (peak G vs speed: lateral/accel/brake)
  2. Grip Circle (longitudinal vs lateral G scatter)
  3. Cornering Grip vs Speed
  4. Steering Response (steer angle vs lateral G)
- Summary stats: max lateral/accel/brake/combined G, peak lateral speed
- GripAnalysis types + type guard
- car_grip use case in SessionDetailView (quick stats + view button)
- Route /analysis/grip/:id
- Global .grid-4 CSS utility

src/router/index.ts

@@ -30,6 +30,12 @@ const router = createRouter({
       component: () => import('@/views/ShiftPointsView.vue'),
       props: true,
     },
+    {
+      path: '/analysis/grip/:id',
+      name: 'grip-analysis',
+      component: () => import('@/views/GripAnalysisView.vue'),
+      props: true,
+    },
     {
       path: '/tracks',
       name: 'tracks',