feat: Phase 2 — variant strip, while-here, charger swap block

Adds the three big "options" UX wins from Direction B:

1. Route variants (Fastest / Scenic / Cheapest)
   - Grok prompt now returns a top-level variants[] summary with
     drive/charge/cost/distance/pros for each variant, plus a
     selectedVariant indicating which one the stops reflect.
   - VariantStrip renders under the top bar with selected-state
     styling, tone-coloured highlight (red/green/blue) on the most
     relevant stat, and 3-5 pros pills.
   - Clicking a variant fires /api/chat with selectedVariant=<id> so
     Grok re-plans with that variant's bias. A "switching" state
     disables the strip while the request is in flight.
   - The chat route accepts selectedVariant ('fast'|'scenic'|'cheap')
     and the GrokHeadlessClient threads it through both the local CLI
     and xAI API paths.

2. While here (food / do / see / shop / rest)
   - Every Supercharger, destination-charger and hotel stop now
     returns a nearby[] array with category/icon/name/detail.
   - Expanded stop card has tabs (All / Food / Do / See) — tabs
     auto-hide when no items in that category. Two-column grid of
     named places with walk-time + rating, e.g. "M&S Foodhall · 1 min
     walk · 4.3★ · sandwiches".

3. Charger swap block
   - Every charging stop now returns chargerOptions[] with the
     current pick + 1-3 alternatives at the same location, each with
     network (Tesla/Ionity/Allego/Fastned/BP Pulse), stalls, kW,
     pricePerKwh, detourMin and an optional badge (Faster/Cheaper/
     More stalls/Newer).
   - ChargerSwapBlock shows the current charger as a red-tinted
     header row that expands to reveal alternatives with stats and a
     Use button per row.

Renamed the existing AlternativeStop UI label from "alternative(s)"
to "location alternative(s)" so it's clear when the user is swapping
the stop *location* vs swapping the *charger at the same location*.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

server/routes/chat.ts

@@ -12,6 +12,7 @@ const ChatRequestSchema = z.object({
   vehicle: z.object({ name: z.string(), rangeKm: z.number() }),
   itinerary: z.any().optional(),
   history: z.array(z.object({ role: z.enum(['user', 'assistant']), content: z.string() })).optional(),
+  selectedVariant: z.enum(['fast', 'scenic', 'cheap']).optional(),
 });
 
 router.post('/chat', async (req, res) => {
@@ -27,7 +28,7 @@ router.post('/chat', async (req, res) => {
       return res.status(400).json({ error: 'Invalid request' });
     }
 
-    const { message, vehicle, itinerary, history = [] } = parsed.data;
+    const { message, vehicle, itinerary, history = [], selectedVariant = 'fast' } = parsed.data;
 
     log.info({
       requestId,
@@ -35,13 +36,15 @@ router.post('/chat', async (req, res) => {
       vehicle: vehicle.name,
       historyLength: history.length,
       currentItineraryDays: itinerary?.days?.length || 0,
+      selectedVariant,
     }, 'Parsed chat request');
 
     // Call Grok (this will produce very detailed logs inside GrokHeadlessClient)
     const result = await grok.chat(
       [...history, { role: 'user' as const, content: message }],
       itinerary,
-      vehicle
+      vehicle,
+      selectedVariant,
     );
 
     const duration = Date.now() - start;
@@ -50,6 +53,12 @@ router.post('/chat', async (req, res) => {
     if (result.updatedItinerary) {
       payload.itinerary = result.updatedItinerary;
     }
+    if (result.variants && Array.isArray(result.variants)) {
+      payload.variants = result.variants;
+    }
+    if (result.selectedVariant) {
+      payload.selectedVariant = result.selectedVariant;
+    }
 
     log.info({
       requestId,