Add Plot Profile command

[yangfei]

Summary

Add a first Plot Profile command for common ImageJ-style intensity inspection.

Scope

• Define the first supported profile source clearly.
• Compute profile values in core code where practical.
• Show a simple plot window in the app.
• Keep the first version limited rather than trying to cover every ROI type.

Acceptance criteria

• User can run Plot Profile on the supported selection type.
• The profile window shows intensity values clearly.
• Core profile calculation has automated tests.
• Unsupported selection types fail clearly or keep the command disabled.