feat: expanded smart folder category coverage (Gaming, RideSharing, FoodDelivery, SeasonalSales, Wellness, Shopping)

- Added 6 new EmailCategory enum values
- HeuristicClassifier rewritten with domain and subject-keyword rules:
  - RideSharing: Uber, Lyft, Bolt, Free Now, Grab etc.
  - FoodDelivery: DoorDash, Uber Eats, Deliveroo, Just Eat, Grubhub etc.
  - Gaming: Steam, Epic, EA, Xbox, PlayStation, Nintendo, Blizzard, Riot etc.
  - Shopping: Amazon, eBay, Etsy, ASOS, Zalando, Shein etc.
  - SeasonalSales: subject keywords (sale, % off, promo, black friday etc.)
  - Wellness: Strava, Garmin, Peloton, MyFitnessPal, Headspace, Nike etc. + subject hints
  - Priority ordering prevents ride-share/food receipts misclassifying as Finance
- SidebarCounts maps all new slugs to their EmailCategory
- frontend folderToRequest() and CAT_SLUG map all new categories
- Existing emails will pick up new categories on next sync

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/InboxIntel.Infrastructure/Analytics/AnalyticsService.cs

@@ -167,16 +167,16 @@ public class AnalyticsService : IAnalyticsService
 
         var smartFolders = new Dictionary<string, int>
         {
-            ["automated"] = Cat(EmailCategory.Notification),
-            ["finance"]   = Cat(EmailCategory.Finance),
-            ["social"]    = Cat(EmailCategory.Social),
-            ["shopping"]  = Cat(EmailCategory.Promotional),
-            ["noreply"]   = 0,
-            ["gaming"]    = 0,
-            ["sales"]     = 0,
-            ["ridesharing"] = 0,
-            ["food"]      = 0,
-            ["wellness"]  = 0,
+            ["automated"]   = Cat(EmailCategory.Notification),
+            ["finance"]     = Cat(EmailCategory.Finance),
+            ["social"]      = Cat(EmailCategory.Social),
+            ["shopping"]    = Cat(EmailCategory.Shopping) + Cat(EmailCategory.Promotional),
+            ["noreply"]     = Cat(EmailCategory.Notification),
+            ["gaming"]      = Cat(EmailCategory.Gaming),
+            ["sales"]       = Cat(EmailCategory.SeasonalSales),
+            ["ridesharing"] = Cat(EmailCategory.RideSharing),
+            ["food"]        = Cat(EmailCategory.FoodDelivery),
+            ["wellness"]    = Cat(EmailCategory.Wellness),
         };
 
         return new SidebarCountsDto(inbox, allMail, unread, starred, sent, drafts, trash, spam, large, old, smartFolders);