Phase 4: Past appointments + AI prediction demo data

- Appointments: add ~25 past appointments (last 90 days) with Completed,
  Cancelled, No Show, and Rescheduled statuses; completed records carry
  ActualStartTime/ActualEndTime with realistic variance; cancel/no-show
  notes explain why; customer label falls back to ContactFirst/LastName
  for residential customers
- Fix future appointment title for residential customers (was always using
  CompanyName which is null for individuals)
- New SeedDataService.AiPredictions.cs: seeds 8 AiItemPrediction records
  (varied complexity/confidence/tags/reasoning) and attaches them to the
  first 8 eligible QuoteItems, marking those items IsAiItem=true; 3 of 8
  have UserOverrodeEstimate=true for AI Accuracy report demo
- SeedDataService.cs: wire SeedAiPredictionsAsync after Invoices
- Remove.cs: collect QuoteItem.AiPredictionId FKs before deleting items,
  then delete orphaned AiItemPrediction records after quotes are removed

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

src/PowderCoating.Infrastructure/Services/SeedDataService.cs

@@ -425,6 +425,7 @@ public partial class SeedDataService : ISeedDataService
         await RunSeeder("Time entries",   details, errors, result, () => SeedJobTimeEntriesAsync(company));
         await RunSeeder("Inv. txns",      details, errors, result, () => SeedInventoryTransactionsAsync(company));
         await RunSeeder("Invoices",       details, errors, result, () => SeedInvoicesAsync(company));
+        await RunSeeder("AI predictions", details, errors, result, () => SeedAiPredictionsAsync(company));
         await RunSeeder("Vendor bills",   details, errors, result, () => SeedBillsAsync(company));
         await RunSeeder("Expenses",       details, errors, result, () => SeedExpensesAsync(company));
         await RunSeeder("Appointments",   details, errors, result, () => SeedAppointmentsAsync(company));