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/domain/subscriptions.service.ts

@@ -15,7 +15,9 @@ import {
   BillingCycle,
   SubscriptionStatus,
   UpdateSubscriptionData,
+  NeedsVehicleSelectionResponse,
 } from './subscriptions.types';
+import { VehiclesRepository } from '../../vehicles/data/vehicles.repository';
 
 interface StripeWebhookEvent {
   id: string;
@@ -27,6 +29,7 @@ interface StripeWebhookEvent {
 
 export class SubscriptionsService {
   private userProfileRepository: UserProfileRepository;
+  private vehiclesRepository: VehiclesRepository;
 
   constructor(
     private repository: SubscriptionsRepository,
@@ -34,6 +37,7 @@ export class SubscriptionsService {
     pool: Pool
   ) {
     this.userProfileRepository = new UserProfileRepository(pool);
+    this.vehiclesRepository = new VehiclesRepository(pool);
   }
 
   /**
@@ -57,6 +61,65 @@ export class SubscriptionsService {
     }
   }
 
+  /**
+   * Check if user needs to make a vehicle selection after auto-downgrade
+   * Returns true if: user is on free tier, has >2 vehicles, and hasn't made selections
+   */
+  async checkNeedsVehicleSelection(userId: string): Promise<NeedsVehicleSelectionResponse> {
+    const FREE_TIER_VEHICLE_LIMIT = 2;
+
+    try {
+      // Get current subscription
+      const subscription = await this.repository.findByUserId(userId);
+
+      // No subscription or not on free tier = no selection needed
+      if (!subscription || subscription.tier !== 'free') {
+        return {
+          needsSelection: false,
+          vehicleCount: 0,
+          maxAllowed: FREE_TIER_VEHICLE_LIMIT,
+        };
+      }
+
+      // Count user's active vehicles
+      const vehicleCount = await this.vehiclesRepository.countByUserId(userId);
+
+      // If within limit, no selection needed
+      if (vehicleCount <= FREE_TIER_VEHICLE_LIMIT) {
+        return {
+          needsSelection: false,
+          vehicleCount,
+          maxAllowed: FREE_TIER_VEHICLE_LIMIT,
+        };
+      }
+
+      // Check if user already has vehicle selections
+      const existingSelections = await this.repository.findVehicleSelectionsByUserId(userId);
+
+      // If user already made selections, no selection needed
+      if (existingSelections.length > 0) {
+        return {
+          needsSelection: false,
+          vehicleCount,
+          maxAllowed: FREE_TIER_VEHICLE_LIMIT,
+        };
+      }
+
+      // User is on free tier, has >2 vehicles, and hasn't made selections
+      return {
+        needsSelection: true,
+        vehicleCount,
+        maxAllowed: FREE_TIER_VEHICLE_LIMIT,
+      };
+    } catch (error: any) {
+      logger.error('Failed to check needs vehicle selection', {
+        userId,
+        error: error.message,
+      });
+      throw error;
+    }
+  }
+
   /**
    * Create new subscription (Stripe customer + initial free tier record)
    */