ci: fix web search test hangs

[franciscojavierarceo]

Summary

• align the remaining You.com test mocks with the GET query-parameter contract introduced in fix: use GET query params for You.com search #203
• bound mock request captures so future contract mismatches fail within five seconds instead of hanging CI
• verify the intentional 500 search mock is actually reached and cap the Rust job at 30 minutes

Test Plan

• cargo fmt --all -- --check
• cargo clippy --all-targets -- -D warnings
• cargo build
• cargo test
• cargo test -p agentic-server-core --test dispatch_loop_cassette_test
• cargo test -p agentic-server-core --test messages_loop_test
• cargo test -p agentic-server-core --test messages_stream_test