Agents: Add smaller max width to workspace and harness pickers

[hawkticehurst]

We should set a max width on very long workspace names in the agent window new chat view workspace picker so it doesn't result in a highly compressed harness picker. More specifically:

• Set a max width on workspace picker
• Set a max width on harness picker
• Stretch: Apply middle ellipsis truncation so you can see the end of the workspace path (instead of path being cut off at the end)