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.Application/Data/DiplomaMills.cs

@@ -135,24 +135,6 @@ public static class DiplomaMills
         "distance learning university", // be careful - some are legit
     ];
 
-    /// <summary>
-    /// Fake accreditation bodies used by diploma mills.
-    /// </summary>
-    public static readonly HashSet<string> FakeAccreditors = new(StringComparer.OrdinalIgnoreCase)
-    {
-        "World Association of Universities and Colleges",
-        "WAUC",
-        "International Accreditation Agency",
-        "Universal Accreditation Council",
-        "Board of Online Universities Accreditation",
-        "International Council for Open and Distance Education",
-        "World Online Education Accrediting Commission",
-        "Central States Consortium of Colleges and Schools",
-        "American Council of Private Colleges and Universities",
-        "Association of Distance Learning Programs",
-        "International Distance Education Certification Agency",
-    };
-
     /// <summary>
     /// Check if an institution is a known diploma mill.
     /// </summary>
@@ -196,15 +178,4 @@ public static class DiplomaMills
 
         return false;
     }
-
-    /// <summary>
-    /// Check if an accreditor is known to be fake.
-    /// </summary>
-    public static bool IsFakeAccreditor(string accreditorName)
-    {
-        if (string.IsNullOrWhiteSpace(accreditorName))
-            return false;
-
-        return FakeAccreditors.Contains(accreditorName.Trim());
-    }
 }