Consolidate scattered `X-Real-IP` / `request.client.host` fallback logic into the single `client_ip()` helper from `utils`, reducing duplication in the rate limiter middleware, project file zip routes, tools shared module, and audit record builder. Also refactor three admin endpoints (`/ai-usage/data`, `/analytics`, `/users/{uid}/ai-usage`) to use the existing `require_admin()` guard instead of repeating manual auth checks, and remove now-unused `get_current_user`/`is_admin` imports from those modules.
