v0.24.0 - Cap Truncated Validate Error Messages

Fixed

• validate: ValidationErrorEntry.message is now capped at 300
  characters (_MAX_VALIDATE_ERROR_CHARS, plus a trailing
  "... (truncated)" suffix when truncation occurs) instead of reusing
  the caught exception's str() verbatim without limit -- a structurally
  malformed document (e.g. an unexpected/duplicate heading) could
  otherwise produce a message several hundred characters long once
  wrap_tool_errors's domain/tool/channel label was prepended. Also fixed
  models/md/_markdown.py::not_in_mdformat_message()'s global-mismatch
  (line_no == 0) branch, which embedded the full raw text/formatted
  via repr() with no bound -- it now routes both through the existing
  snippet() helper, matching every sibling message-builder in that
  module (GitHub issue #110).