fix(learn): ignore parallel tool call cancellations

[houtinghang]

Summary

• Ignore Claude Code parallel tool-call cancellations during rtk learn error classification.
• Add a regression test based on the reported cancellation payload to ensure sibling parallel commands are not emitted as CLI corrections.

Root cause

is_command_error filtered explicit user-rejection phrases, but did not recognize:

<tool_use_error>Cancelled: parallel tool call Bash(...) errored</tool_use_error>

Because the payload contains errored, it passed the generic error-content check. find_corrections then treated the next sibling command as a successful replacement and generated a false Use X not Y rule.

Impact

Cancelled parallel work is now excluded before correction pairing, preventing false rules from dominating generated cli-corrections.md files.

Fixes #1659.

Validation

• cargo test learn::detector::tests:: -- --nocapture — 16 passed.
• cargo fmt --all --check — passed.
• cargo clippy --all-targets — passed.
• Full local Windows run: 2,404 passed; 30 existing environment-dependent tests failed because the sandbox blocks %APPDATA% writes or expects Unix commands. No learn tests failed.

[CLAassistant]

All committers have signed the CLA.