Add retry command parser coverage

[JacKane21]

Summary

• add regression coverage that interactive /retry parses to AppCommand::Retry
• add coverage for the /r alias
• assert retry remains listed in the default interactive commands

The current runtime path already retries by calling UI::on_message(None), matching the maintainer note on #389. This PR locks the exposed command surface down so that behavior stays reachable from the chat prompt.

Verification

• cargo test -p forge_main retry
• git diff --check

Note: cargo fmt --check currently reports an unrelated existing formatting diff in crates/forge_main/src/info.rs, so I did not include that file in this PR.

/claim #389

[CLAassistant]

All committers have signed the CLA.

[JacKane21]

@algora-pbc /claim #389

The PR body also includes /claim #389; adding this explicit comment in case the claim bot needs a comment trigger on the renamed tailcallhq/forgecode repository.

[JacKane21]

Hi maintainers, the contributor has signed the CLA, but the CLAassistant status on this PR still shows not_signed. I tried the recheck link from a signed-in GitHub browser session and it redirected back to the GitHub dashboard without updating the status. Could you please rerun or check the CLA status from your side when you get a chance? Thanks.

[JacKane21]

Update: CLAassistant now shows all committers have signed the CLA, and the current visible check is passing. Thanks.