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/Models/GitHubVerificationResult.cs

@@ -37,9 +37,6 @@ public sealed record SkillVerification
     public required string ClaimedSkill { get; init; }
     public required bool IsVerified { get; init; }
     public int RepoCount { get; init; }
-    public int TotalLinesOfCode { get; init; }
-    public DateOnly? FirstUsed { get; init; }
-    public DateOnly? LastUsed { get; init; }
     public string? Notes { get; init; }
 }