Add XML doc to all service interfaces and implementations (#26)

- Update CLAUDE.md: replace incorrect 'no XML doc on internal code' rule
  with the correct convention (XML doc on all public methods and
  non-trivial private/protected helpers)
- Restore /// <summary> on FileDownloadController private helpers
  (HandleRangeRequest, StreamRangeAsync)
- Add full XML doc to all service contracts:
  ICaptchaVerifier, IEmailSender, ICvMatcherService, IJobTextExtractor,
  IJobTokenService, IDocumentClassifier, IRagService, ITextChunker,
  ITextExtractor, IEmailTemplateService, ITemplateService
- Add /// <summary> and /// <inheritdoc /> to all concrete service classes
  and their methods: RecaptchaVerifier, EmailApiEmailSender,
  SmtpEmailDispatcher, CvMatcherService, JobTextExtractor, JobTokenService,
  RagService, DocumentClassifier, TextChunker, TextExtractor,
  HtmlJobSearcher, CvSearchEmailSender, CvSearchJobTask,
  EmailTemplateService, DbTemplateService

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Apis/api/Controllers/FileDownloadController.cs

@@ -131,7 +131,9 @@ namespace Api.Controllers
             }
         }
 
-        // Handles HTTP range requests for partial content downloads and resume support.
+        /// <summary>
+        /// Handles HTTP range requests for partial content downloads and resume support.
+        /// </summary>
         private async Task<IActionResult> HandleRangeRequest(
             string filePath,
             long fileLength,
@@ -188,7 +190,9 @@ namespace Api.Controllers
             }
         }
 
-        // Efficiently streams a specific byte range from source to destination.
+        /// <summary>
+        /// Efficiently streams a specific byte range from source to destination.
+        /// </summary>
         private static async Task StreamRangeAsync(Stream source, Stream destination, long bytesToRead)
         {
             var buffer = new byte[BufferSize];