Fix pricing consistency across Quote → Job → Invoice; add stage-flow tests

- Store complete PricingBreakdownJson snapshot on Job at every save point so
  the Details page reads stored data rather than re-running the pricing engine
- Add 7 missing fields to Quote entity (FacilityOverheadCost, tier/quote discounts,
  SubtotalAfterDiscount) and persist them via ApplyPricingSnapshot
- Fix OvenCostId-as-rate bug in JobsController (FK was passed as decimal $/hr)
- Fix hardcoded LaborCost * 0.4 multiplier in two JobItemAssemblyService overloads
- Fix FacilityOverheadCost dropped from invoices in both quote and direct-job paths
- Fix RushFee missing from direct-job invoices (read from PricingBreakdownJson)
- Fix Notes and CatalogItemId not copied to InvoiceItem
- Add 14 unit tests in PricingStageFlowTests covering all three pricing stages

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

tests/PowderCoating.UnitTests/JobItemAssemblyServiceTests.cs

@@ -59,7 +59,8 @@ public class JobItemAssemblyServiceTests
         var pricing = new QuoteItemPricingResult
         {
             UnitPrice = 29.99m,
-            TotalPrice = 59.98m
+            TotalPrice = 59.98m,
+            LaborCost = 23.992m    // explicitly from pricing engine, not a 0.4× multiplier
         };
 
         var jobItem = _service.CreateJobItem(source, jobId: 10, companyId: 3, pricing: pricing, createdAtUtc: CreatedAtUtc);