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/Contracts/ITextChunker.cs

@@ -1,6 +1,17 @@
 namespace Api.Services.Contracts;
 
+/// <summary>
+/// Splits document text into overlapping chunks suitable for embedding and vector search.
+/// </summary>
 public interface ITextChunker
 {
+    /// <summary>
+    /// Divides <paramref name="text"/> into a list of chunks using a sliding window.
+    /// Adjacent chunks share <paramref name="overlap"/> characters to preserve cross-boundary context.
+    /// </summary>
+    /// <param name="text">The full document text to chunk.</param>
+    /// <param name="chunkSize">Maximum character length per chunk (clamped to 300–3000).</param>
+    /// <param name="overlap">Number of trailing characters from the previous chunk to repeat at the start of the next (clamped to 0–chunkSize/2).</param>
+    /// <returns>Ordered list of non-empty text chunks.</returns>
     IReadOnlyList<string> Chunk(string text, int chunkSize, int overlap);
 }