refactor: unify inquiry status strings using constants (P1-06)

Problem: Inquiry status values were hardcoded as strings in multiple places:
- InquiryList.razor: Status="new", Status="consulting", etc.
- InquiryDetail.razor: inquiry.Status = "consulting"
- Makes it error-prone to update status values globally

Solution:
- Add public const fields to InquiryStatusMapper for all status values
- Replace hardcoded strings with constants (StatusNew, StatusConsulting, etc.)
- InquiryList and InquiryDetail now use mapper constants

Result: Single source of truth for status values. Changing a status value now
requires only updating InquiryStatusMapper, and all usages automatically update.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

src/TaxBaik.Application/Services/InquiryStatusMapper.cs

@@ -4,6 +4,13 @@ using TaxBaik.Domain.Enums;
 
 public static class InquiryStatusMapper
 {
+    // Status storage values (database)
+    public const string StatusNew = "new";
+    public const string StatusConsulting = "consulting";
+    public const string StatusContracted = "contracted";
+    public const string StatusRejected = "rejected";
+    public const string StatusClosed = "closed";
+
     public static readonly Dictionary<string, string> Labels = new()
     {
         ["new"]        = "신규",