chore(design-client): type parseThemeFromDesign response

[serge-sedelnikov]

Summary

• Bump @epilot/design-client to 0.5.4
• Replace the untyped type: object response of the parseThemeFromDesign endpoint with a new ParseThemeFromDesignResp schema
• New schema exposes theme (Theme) and design (ItemMetada + DesignItem + Custom_Style + Journey) so consumers get strong typing for the parsed result

Notes

• The branch name and commit message reference ER-4987 / entity-client, but the actual diff is scoped to design-client only. Happy to rename / amend if reviewers prefer.

Test Plan

• Confirm clients/design-client/src/openapi.d.ts regenerates cleanly from the updated openapi.json
• Verify downstream consumers of parseThemeFromDesign pick up the typed ParseThemeFromDesignResp instead of any/object
• CI passes