Upgrade Docusaurus to 3.9.2 and update markdown config

[yumechi]

Summary

This PR upgrades Docusaurus and related dependencies to version 3.9.2, updates the markdown configuration to use the new hooks API, and simplifies pnpm dependency overrides.

Key Changes

• Docusaurus upgrade: Updated all @docusaurus/* packages from 3.8.1 to 3.9.2
  • Core, preset-classic, and google-gtag plugin
  • Type definitions and module aliases
• Markdown configuration: Migrated onBrokenMarkdownLinks setting from top-level config to the new markdown.hooks structure, aligning with Docusaurus 3.9.2 API changes
• Dependency overrides: Simplified pnpm overrides from 8 entries to a single targeted override for gray-matter>js-yaml, reducing maintenance burden and improving clarity
• Lock file: Updated pnpm-lock.yaml to reflect new dependency versions

Implementation Details

The onBrokenMarkdownLinks configuration was moved into a nested markdown.hooks object as part of Docusaurus 3.9.2's restructuring of markdown-related settings. This change maintains the same behavior while following the new configuration schema.