Add TCPA-compliant SMS consent tracking for prospect quotes

- Quote entity: ProspectSmsConsent (bool) + ProspectSmsConsentedAt (DateTime?) fields
- QuoteDtos: consent fields on Create/Update/Convert DTOs with TCPA guidance text
- Quote Create/Edit views: SMS consent checkbox shown when mobile number is entered
- Quote ConvertToCustomer view: staff must re-confirm consent carries over to customer record
- QuoteApproval: consent state exposed in ViewModel and ApprovalPage for transparency
- Consent timestamp cleared when prospect quote is linked to an existing customer
- Migration: AddProspectSmsConsent

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

src/PowderCoating.Core/Entities/Quote.cs

@@ -17,6 +17,9 @@ public class Quote : BaseEntity
     public string? ProspectCity { get; set; }
     public string? ProspectState { get; set; }
     public string? ProspectZipCode { get; set; }
+    // TCPA compliance: only true when staff explicitly records verbal SMS consent
+    public bool ProspectSmsConsent { get; set; } = false;
+    public DateTime? ProspectSmsConsentedAt { get; set; }
 
     // Lookup foreign key (replacing enum)
     public int QuoteStatusId { get; set; }