wait until rate-limit reset time before retrying

[jbj338033]

Summary

On a rate-limit (429), wait until the provider-reported reset time and resume automatically instead of giving up after a fixed backoff, so conversations survive Anthropic subscription 5h/weekly limits and any provider that reports a reset window. A long relative retry_after is promoted to a precise wall-clock wait; absolute reset headers are parsed on the 429 error path in the SDK.

Verification

• cargo fmt --all --check — passed
• cargo clippy --workspace --all-targets -- -D warnings — passed
• cargo test --workspace — passed

Note

Depends on goat-sdk rev 4337282 (branch feat/ratelimit-reset-on-error), which adds resets_at to StreamError::RateLimited and Event::Retrying and parses reset headers on the 429 path. Bumps PROTOCOL_VERSION 6 → 7.