[TASK] Align frontend with the updated backend API contract

[Antoni-Czaplicki]

Note

🤖 [gpt-5.6-sol] creating this issue on behalf of Antek

Align the frontend API integration with the backend changes completed in Solvro/backend-testownik#241.

Scope:

• Update shared API error handling to support the standardized envelope: type and errors[], with code, detail, and attr on every error item.
• Audit existing frontend calls that still expect legacy error, detail, or raw serializer-error payloads.
• Integrate and type the newly added AI usage, limits, model catalog, chat-history, and administration endpoints needed by the frontend.
• Preserve the intentional structured quota-decision responses returned from AI quota checks for HTTP 409 and 429; these are domain responses, not standardized error envelopes.
• Regenerate or reconcile API types from the current OpenAPI schema and remove obsolete local response types.
• Verify authentication, permissions, validation, not-found, upload, Wrapped, grades, feedback, and account-management error states in the UI.

Backend reference: Solvro/backend-testownik#241

Acceptance criteria:

• Existing and new API calls compile against the current backend contract.
• User-facing error states use code/detail/attr without relying on legacy response shapes.
• New AI-related screens and flows can consume all required backend endpoints.
• Frontend tests cover representative 400, 401, 403, 404, 409, and 429 responses.