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>

src/PowderCoating.Core/Entities/Job.cs

@@ -66,6 +66,10 @@ public class Job : BaseEntity
     // Used to detect when the quote was subsequently edited so the job details page can warn the user.
     public DateTime? QuoteSnapshotUpdatedAt { get; set; }
 
+    // Pricing snapshot — serialized QuotePricingBreakdownDto stored at save time so Details displays
+    // the breakdown that was actually calculated, not a re-run against current operating costs.
+    public string? PricingBreakdownJson { get; set; }
+
     // Rework tracking
     public bool IsReworkJob { get; set; }
     public int? OriginalJobId { get; set; }       // Set when this job was created as a rework