Sync Core API docs and WebGUI roadmap

[foxly-it]

What changed

• pin the merged rootguard-core API documentation revision
• record the delivered authenticated Core API reference in the persistent project state
• add the agreed accessible WebGUI navigation and appearance slice to the canonical roadmap
• define acceptance criteria for the utility header, bilingual settings search, System/Light/Dark modes, sticky collapsed sidebar, responsive behavior, and WCAG-oriented verification

Component PR

• Document authenticated Core API endpoints rootguard-core#35

Validation

• Core CI passed on the merged component revision
• git diff --check