fix index out range error while handling idling

[plusiv]

This pull request makes minor adjustments to the development setup and improves the robustness of the IMAP IDLE command handling.

Development environment update:

• Updated the program path in .vscode/launch.json to point to the cmd/mokapi directory instead of the main.go file, which may allow linking help.go file in build process.

IMAP protocol handling improvement:

• Simplified the check for the "DONE" command in the handleIdle function in imap/idle.go to directly compare the input line, making the code more straightforward and potentially reducing parsing errors.

Ref: https://www.rfc-editor.org/rfc/rfc2177#section-3

[marle3003]

Thank you for your contribution and for submitting this PR!
I fixed the test, everything is passing now.