Add quote-changed banner with re-sync to job details

When a source quote is edited after a job was created from it, the job
details page now shows a warning banner with the date of the change and
a link to the quote. Two actions are offered:

- Re-sync from Quote: replaces all job items, coats, prep services, and
  pricing from the current quote. Only available while the job is still
  in a pre-production status (Pending, Quoted, Approved); hidden once
  shop work has started (InPreparation or beyond).
- Dismiss: acknowledges the change without altering the job, clearing
  the banner by advancing the stored snapshot timestamp.

Implemented via Job.QuoteSnapshotUpdatedAt (new nullable column), set at
quote→job conversion time. The banner fires when quote.UpdatedAt exceeds
this baseline. Migration: AddJobQuoteSnapshotUpdatedAt.

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

src/PowderCoating.Web/Controllers/QuotesController.cs

@@ -2991,7 +2991,8 @@ public class QuotesController : Controller
             DiscountValue = quote.DiscountValue,
             DiscountReason = quote.DiscountReason,
             CompanyId = quote.CompanyId,
-            CreatedAt = DateTime.UtcNow
+            CreatedAt = DateTime.UtcNow,
+            QuoteSnapshotUpdatedAt = quote.UpdatedAt ?? quote.CreatedAt
         };
 
         await _unitOfWork.Jobs.AddAsync(job);