Fix two production billing bugs: invoice missing oven cost, quote stuck in Draft after send

Bug 1 — Invoice total didn't match job total for direct jobs:
- Root cause: all three item-save paths in JobsController passed null for
  ovenCostId, so FinalPrice/ShopSuppliesAmount were stored without oven cost
  while the Details page recalculated live with OvenCostId and showed higher.
- Add OvenBatchCost stored field to Job entity (migration AddJobOvenBatchCost,
  default 0 for existing rows).
- Fix Create, Edit, and UpdateItems to pass job.OvenCostId and save OvenBatchCost.
- Fix InvoicesController.Create GET for direct jobs to use stored OvenBatchCost
  and ShopSuppliesAmount as separate labeled lines instead of recalculating
  shop supplies from scratch (which excluded the oven cost base).

Bug 2 — Quote status stayed Draft after "Send Quote via Email":
- ResendQuote advanced the approval token and sent the email but never
  updated the status. Added Draft → Sent advancement (same guard used by
  the SMS send path) so the status updates on successful email send.

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

src/PowderCoating.Core/Entities/Job.cs

@@ -28,6 +28,7 @@ public class Job : BaseEntity
     // Pricing
     public decimal QuotedPrice { get; set; }
     public decimal FinalPrice { get; set; }
+    public decimal OvenBatchCost { get; set; }
     public decimal ShopSuppliesAmount { get; set; }
     public decimal ShopSuppliesPercent { get; set; }