Exclude trial companies from MRR/ARR and revenue trend

Companies with null StripeSubscriptionId are on trial and have no real
subscription income. They were being counted as paying Active/GracePeriod
customers, inflating MRR, ARR, plan distribution, and 12-month trend.

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

src/PowderCoating.Web/Controllers/RevenueController.cs

@@ -74,9 +74,10 @@ public class RevenueController : Controller
 
         // ── Revenue metrics ──────────────────────────────────────────────
 
-        // Active paying companies
+        // Active paying companies — exclude trials (no StripeSubscriptionId = on trial)
         var payingActive = companies
             .Where(c =>
+                        !string.IsNullOrEmpty(c.StripeSubscriptionId) &&
                         (c.SubscriptionStatus == SubscriptionStatus.Active ||
                          c.SubscriptionStatus == SubscriptionStatus.GracePeriod))
             .ToList();
@@ -111,6 +112,7 @@ public class RevenueController : Controller
         // ── Plan distribution ────────────────────────────────────────────
         var planDistribution = companies
             .Where(c => !c.IsComped &&
+                        !string.IsNullOrEmpty(c.StripeSubscriptionId) &&
                         (c.SubscriptionStatus == SubscriptionStatus.Active ||
                          c.SubscriptionStatus == SubscriptionStatus.GracePeriod))
             .GroupBy(c => c.SubscriptionPlan)
@@ -137,6 +139,7 @@ public class RevenueController : Controller
             var activeInMonth = companies
                 .Where(c =>
                     !c.IsComped &&
+                    !string.IsNullOrEmpty(c.StripeSubscriptionId) &&
                     c.CreatedAt < monthEnd &&
                     (c.SubscriptionStatus == SubscriptionStatus.Active ||
                      c.SubscriptionStatus == SubscriptionStatus.GracePeriod ||