fix: preserve cancelled shell command tool results

[oz-for-oss]

Closes #13251

Summary

• Preserve command text for cancelled run_shell_command results.
• Send cancelled request-command results back to the API as explicit RunShellCommandResult tool results instead of dropping them.
• Update restored conversation, shell-command execution, UI, and SDK output paths for the new cancellation result shape.

Validation

• cargo test --manifest-path /workspace/warp/Cargo.toml -p ai cancelled_request_command_converts_to_explicit_tool_result
• cargo test --manifest-path /workspace/warp/Cargo.toml -p warp test_into_exchanges_with_tool_calls_and_cancellation
• cargo fmt --manifest-path /workspace/warp/Cargo.toml --all --check
• cargo check --manifest-path /workspace/warp/Cargo.toml -p warp --lib

Notes

• No approved spec context was attached for this issue.
• The requested GitHub context fetch script was not present in the checkout/workspace, so the issue body/comments could not be fetched through that mandated script.

Conversation: https://app.warp.dev/conversation/b4ab29ea-b7a7-4c27-83d4-ebc3257b32c5
Run: https://oz.warp.dev/runs/019f1ac3-0710-7729-8001-f2af1227e47f
This PR was generated with Oz.