chore: add markdownlint on pre-commit hook and lint md files

[dingo4dev]

Summary

Add markdownlint on pre-commit hook for linting and formatting markdown files

• .markdownlint.yaml: Added markdown linting rules with configurations for unordered list style, indentation, line length, inline HTML, and more.
• .pre-commit-config.yaml: Integrated markdownlint-cli2 into pre-commit hooks for automated markdown linting and fixing.

Motivation and Context

To style all documentation files and ensure that everyone adheres to the same standards

How Has This Been Tested?

Run pre-commit run --all-files

Types of changes

• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

[Copilot]

Pull Request Overview

This PR introduces markdownlint into the pre-commit workflow and applies linting fixes to markdown files to enforce consistent documentation style.

• Add .markdownlint.yaml with project-specific markdownlint rules.
• Integrate markdownlint-cli2 into .pre-commit-config.yaml for automated markdown linting and fixing.
• Adjust formatting across example READMEs and root docs (remove stray list markers, normalize blank lines, angle-bracket links).

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
.pre-commit-config.yaml	Added markdownlint-cli2 hook for markdown linting (--fix).
.markdownlint.yaml	Defined markdownlint rules (list style, indentation, line length, inline HTML, etc.).
examples/servers/simple-streamablehttp/README.md	Removed stray list items and fixed blank-line spacing.
examples/servers/simple-streamablehttp-stateless/README.md	Deleted extra blank list entries and corrected spacing.
examples/servers/simple-auth/README.md	Normalized list markers, removed double-dash item, and added blank lines before sections.
examples/clients/simple-chatbot/README.MD	Inserted blank lines around code and note blocks.
SECURITY.md	Added blank line after the top-level heading.
README.md	Added blank lines before code blocks and example lists.
CODE_OF_CONDUCT.md	Wrapped email and URLs in angle brackets for link syntax.
CLAUDE.md	Inserted blank lines around commit trailer examples.