[TASK] Refactor A2A error parsing onto the ADK typed errors #1547

Summary

inference-gateway/adk now returns typed errors from client.Client (inference-gateway/adk#400, closes inference-gateway/adk#398): *types.JSONRPCError implements error and unwraps to a sentinel per spec code (types.ErrMethodNotFound, types.ErrTaskNotFound, ...), and the unexpected-status sites return *types.HTTPStatusError{Operation, StatusCode, Body}. The message text is unchanged, so nothing breaks today - but the three text parsers in internal/protocols/a2a/infrastructure/auth.go can be replaced with errors.As / errors.Is once the CLI bumps its ADK dependency.

The parsers to retire: the unexpected status code ... 401|403 regex, the guardrail refusal envelope regex, and the (code: -32601) substring match added in #1545.

Acceptance Criteria

• Bump the github.com/inference-gateway/adk dependency to the release containing the typed errors
• Replace the status-code regex with errors.As(err, &statusErr) and a check on statusErr.StatusCode
• Replace the (code: -32601) substring match with errors.Is(err, types.ErrMethodNotFound)
• Re-check the guardrail envelope parser against the typed error's Data field and drop the regex if it is covered