Add CRM features: Outstanding Pickups, Customer Notes, Clone Job, Preferred Powders

- Outstanding Pickups card on Customer Details shows jobs awaiting pickup with age badges
- Customer Notes log: inline add/delete notes with important flag, AJAX-backed
- Clone Job action on Jobs controller; Repeat Last Job button on Customer Details quick actions
- Preferred Powders per customer: typeahead inventory search, AJAX add/remove
- CustomerPreferredPowder entity + migration; unit tests for CRM stats/timeline logic
- Fix EF Core concurrency bug: parallel Task.WhenAll FindAsync replaced with sequential awaits

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

src/PowderCoating.Core/Entities/SupportingEntities.cs

@@ -152,6 +152,20 @@ public class CustomerNote : BaseEntity
     public virtual Customer Customer { get; set; } = null!;
 }
 
+/// <summary>
+/// Records an inventory item as a preferred powder for a specific customer.
+/// Shown on Customer Details for faster quoting of repeat orders.
+/// </summary>
+public class CustomerPreferredPowder : BaseEntity
+{
+    public int CustomerId { get; set; }
+    public int InventoryItemId { get; set; }
+    public string? Notes { get; set; }
+
+    public virtual Customer Customer { get; set; } = null!;
+    public virtual InventoryItem InventoryItem { get; set; } = null!;
+}
+
 public class JobStatusHistory : BaseEntity
 {
     public int JobId { get; set; }