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>

CLAUDE.md

@@ -212,8 +212,8 @@ Every service follows this structure:
 
 ## Coding conventions
 
-- No XML doc comments on internal code; Swagger annotations on public controller actions
-- No explanatory inline comments — code should be self-describing
+- XML doc comments (`/// <summary>`) on all public methods, interfaces, and non-trivial private/protected helpers; Swagger annotations on public controller actions
+- Inline `//` comments for non-obvious logic; avoid restating what the code already says clearly
 - Use `$$"""..."""` raw string literals (not `$"""`) when the content contains CSS or other curly-brace-heavy text — avoids CS9006 brace-escaping errors
 - `sealed` on all concrete service classes
 - Settings classes injected via `IOptions<T>` — registered with `Configure<T>(config.GetSection("..."))`