Adds claude-opus-4-7 and claude-opus-4-7[1m] alongside the existing 4.6
entries (4.6 stays default). Opus 4.7 introduces a new "xhigh" effort
level between high and max; the option only surfaces on 4.7 models.
The SDK 0.2.71 effort union doesn't yet include xhigh, so the value is
cast at the assignment site.