feat: add needs-vehicle-selection endpoint (refs #60)

- Add GET /api/subscriptions/needs-vehicle-selection endpoint
- Returns { needsSelection, vehicleCount, maxAllowed }
- Checks: free tier, >2 vehicles, no existing selections

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/features/subscriptions/api/subscriptions.controller.ts

@@ -49,6 +49,28 @@ export class SubscriptionsController {
     }
   }
 
+  /**
+   * GET /api/subscriptions/needs-vehicle-selection - Check if user needs vehicle selection
+   */
+  async checkNeedsVehicleSelection(request: FastifyRequest, reply: FastifyReply): Promise<void> {
+    try {
+      const userId = (request as any).user.sub;
+
+      const result = await this.service.checkNeedsVehicleSelection(userId);
+
+      reply.status(200).send(result);
+    } catch (error: any) {
+      logger.error('Failed to check needs vehicle selection', {
+        userId: (request as any).user?.sub,
+        error: error.message,
+      });
+      reply.status(500).send({
+        error: 'Failed to check needs vehicle selection',
+        message: error.message,
+      });
+    }
+  }
+
   /**
    * POST /api/subscriptions/checkout - Create Stripe checkout session
    */