Do not forget spawned task handles
Forgetting a JoinHandle leaks the task and drops panic propagation.
#Metadata
#Why it matters
`std::mem::forget` on a `tokio::spawn` return value or `JoinHandle` abandons the task without awaiting completion or observing panics.
#Remediation
Store the `JoinHandle`, await it, or use a structured shutdown path.
#Repository path
The generated metadata points to critiq-rules/libs/rules/catalog/rules/rust/rust.correctness.forget-join-handle.rule.yaml.