Implement code review fixes and improvements

- Move admin credentials from hardcoded values to configuration
- Add rate limiting (5/min) to login endpoint for brute force protection
- Extract CleanJsonResponse to shared JsonResponseHelper class
- Add DateHelpers.MonthsBetween utility and consolidate date calculations
- Update PdfReportService to use ScoreThresholds constants
- Remove 5 unused shared components (EmploymentTable, FlagsList, etc.)
- Clean up unused CSS from MainLayout.razor.css
- Create IPdfReportService interface for better testability
- Add authentication requirement to Hangfire dashboard in development
- Seal EducationVerifierService class

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

src/TrueCV.Infrastructure/Services/CVParserService.cs

@@ -10,6 +10,7 @@ using TrueCV.Application.Helpers;
 using TrueCV.Application.Interfaces;
 using TrueCV.Application.Models;
 using TrueCV.Infrastructure.Configuration;
+using TrueCV.Infrastructure.Helpers;
 using UglyToad.PdfPig;
 
 namespace TrueCV.Infrastructure.Services;
@@ -191,7 +192,7 @@ public sealed class CVParserService : ICVParserService
         }
 
         // Clean up response - remove markdown code blocks if present
-        responseText = CleanJsonResponse(responseText);
+        responseText = JsonResponseHelper.CleanJsonResponse(responseText);
 
         _logger.LogDebug("Received response from Claude API, parsing JSON");
 
@@ -213,28 +214,6 @@ public sealed class CVParserService : ICVParserService
         }
     }
 
-    private static string CleanJsonResponse(string response)
-    {
-        var trimmed = response.Trim();
-
-        // Remove markdown code blocks
-        if (trimmed.StartsWith("```json", StringComparison.OrdinalIgnoreCase))
-        {
-            trimmed = trimmed[7..];
-        }
-        else if (trimmed.StartsWith("```"))
-        {
-            trimmed = trimmed[3..];
-        }
-
-        if (trimmed.EndsWith("```"))
-        {
-            trimmed = trimmed[..^3];
-        }
-
-        return trimmed.Trim();
-    }
-
     private static CVData MapToCVData(ClaudeCVResponse response)
     {
         return new CVData