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/rag-api/Services/TextChunker.cs

@@ -2,8 +2,12 @@ using Api.Services.Contracts;
 
 namespace Api.Services;
 
+/// <summary>
+/// Splits text into overlapping fixed-size chunks using a sliding window for use in vector embedding pipelines.
+/// </summary>
 public sealed class TextChunker : ITextChunker
 {
+    /// <inheritdoc />
     public IReadOnlyList<string> Chunk(string text, int chunkSize, int overlap)
     {
         if (string.IsNullOrWhiteSpace(text)) return [];