Bound session and update lock waits

[ryanfowler]

Summary

• Added a short bounded wait for session saves so a stuck lock now returns a timeout error instead of hanging forever.
• Added a bounded update-lock wait for explicit self-updates, capped by the request timeout when present and otherwise by a fixed limit.
• Kept nonblocking auto-update checks unchanged and documented the new behavior in AGENTS.md.

Testing

• cargo fmt
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --all-features
• cargo test --all-features --test cli --test formatting --test grpc --test http --test network --test terminal --test update --test websocket -- --test-threads=1