refactor: Remove redundant code and consolidate JsonSerializerOptions

- Remove unused GetRepoLanguagesAsync method from GitHubClient
- Remove unused IsFakeAccreditor and FakeAccreditors from DiplomaMills
- Remove unused CompanyVerificationFlagPenalty constant from ProcessCVCheckJob
- Remove unused SkillVerification properties (TotalLinesOfCode, FirstUsed, LastUsed)
- Remove unused CompanyMatchRequest record from SemanticMatchResult
- Add JsonDefaults.ApiClient and consolidate duplicate JsonSerializerOptions across API clients
- Remove ApiTester tool containing hardcoded API credentials (security fix)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

src/RealCV.Infrastructure/Clients/FcaRegisterClient.cs

@@ -1,8 +1,8 @@
 using System.Net.Http.Json;
-using System.Text.Json;
 using System.Text.Json.Serialization;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
+using RealCV.Application.Helpers;
 
 namespace RealCV.Infrastructure.Clients;
 
@@ -44,7 +44,7 @@ public sealed class FcaRegisterClient
                 return null;
             }
 
-            return await response.Content.ReadFromJsonAsync<FcaIndividualResponse>(JsonOptions);
+            return await response.Content.ReadFromJsonAsync<FcaIndividualResponse>(JsonDefaults.ApiClient);
         }
         catch (Exception ex)
         {
@@ -70,7 +70,7 @@ public sealed class FcaRegisterClient
                 return null;
             }
 
-            var wrapper = await response.Content.ReadFromJsonAsync<FcaIndividualDetailsWrapper>(JsonOptions);
+            var wrapper = await response.Content.ReadFromJsonAsync<FcaIndividualDetailsWrapper>(JsonDefaults.ApiClient);
             return wrapper?.Data?.FirstOrDefault();
         }
         catch (Exception ex)
@@ -94,7 +94,7 @@ public sealed class FcaRegisterClient
                 return null;
             }
 
-            return await response.Content.ReadFromJsonAsync<FcaFirmResponse>(JsonOptions);
+            return await response.Content.ReadFromJsonAsync<FcaFirmResponse>(JsonDefaults.ApiClient);
         }
         catch (Exception ex)
         {
@@ -102,12 +102,6 @@ public sealed class FcaRegisterClient
             return null;
         }
     }
-
-    private static readonly JsonSerializerOptions JsonOptions = new()
-    {
-        PropertyNameCaseInsensitive = true,
-        DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull
-    };
 }
 
 public class FcaOptions