fix(llm): unified rate-limit utilization and status headers are dropped

Description

On an Anthropic subscription account, the rate-limit details parsed out of a response keep
anthropic-ratelimit-unified-5h-reset but drop anthropic-ratelimit-unified-5h-utilization and
anthropic-ratelimit-unified-status, which arrive in the same response.

rateLimitDetails in packages/llm/src/route/executor.ts matches
/^anthropic-ratelimit-(.+)-(limit|remaining|reset)$/. The unified windows report a spent
fraction instead of a remaining count, so -utilization matches nothing and is discarded, and
-status has no branch at all. A rate-limited account is therefore told when its window clears
and never how full it is.

If a response carries only unified headers, limit/remaining/reset all stay empty and the
emptiness check returns undefined, so there are no details at all.

OpenCode version

1.18.31 (dev)

Steps to reproduce

1. Use an Anthropic subscription (OAuth) account, not an API key.
2. Make a request that comes back with the unified headers:
   anthropic-ratelimit-unified-5h-utilization, anthropic-ratelimit-unified-5h-reset,
   anthropic-ratelimit-unified-status.
3. Inspect the parsed HttpRateLimitDetails — the reset is present, the utilization and status are gone.

Operating System

macOS 26.0 (arm64)