feat(site): use display name field for tasks

[ssncferreira]

Description

This PR updates the frontend to use the new display_name field for tasks. In the tasks list view, display_name replaces initial_prompt, and in the tasks sidebar, display_name replaces name. This is a follow-up to #20856, which introduced the display_name field in the backend.

Changes

• Display task.display_name instead of task.initial_prompt in the tasks table
• Display task.display_name instead of task.name in the task sidebar view
• Updated mock data to include display_name for all test tasks
• Added Storybook story to showcase display name rendering with different lengths (short, max length with ellipsis, and edge cases)

Follow-up: #20856
Closes: #20801

[DanielleMaywood]

Approving under the assumption we're happy for the task name to remain where I've drawn the arrow

[mafredri]

LGTM! 👍🏻

Re: @DanielleMaywood's concern, I think the name is more suitable there than the display name (especially considering space constraints), but it could be a bit confusing. I think we can wait for customer feedback on this, though.

[ssncferreira]

Approving under the assumption we're happy for the task name to remain where I've drawn the arrow

I also had that question, but I think it makes sense to keep showing the task name because we already show the display name in the sidebar. This way, the user is able to more easily identify which task name is associated with the task display name.

Additionally, since the workspace name matches the task name, showing the task name in the top bar helps users connect the task to its associated workspace when navigating between views.

Started an internal thread on slack regarding this topic: https://codercom.slack.com/archives/C0992H8HGCS/p1764086497375829