docs(user-guide): add workflow and assistant version history

[bohdanmaliar]

Summary

Adds version history documentation for both workflows and assistants, allowing users to understand how to view, compare, and restore previous versions of their configurations.

Changes

• Added new workflow-version-history.md page documenting how to use the workflow version history feature with screenshots
• Added new assistant-version-history.md page documenting assistant version history functionality with screenshots
• Removed restore-system-instructions.md and consolidated its content into the new assistant version history page
• Updated faq/system-instructions.md to reference the new assistant version history page
• Updated sidebar to include the new version history pages

Testing

• Tested locally with npm start
• All pages render correctly
• Images display properly
• Internal links work
• Sidebar navigation works

Quality Checks

• npm run check passes (typecheck + lint + commitlint)
• No MDX compilation errors
• No raw angle brackets (<text> must be `<text>`)
• Sidebar references document IDs (not filenames)
• Images stored locally next to content (not in static/img/)
• Commit messages follow Conventional Commits
• No secrets or credentials in documentation

[elluvium]

Could you please blur or remove personal details on all screenshots

[bohdanmaliar]

Images were updated