Consolidate task-placeholder terminal with global terminal

[rabanspiegel]

Summary

Currently there are two terminal instances that serve similar purposes:

• task-placeholder - A fallback terminal used when no task is selected
• global - A global terminal that's always available

This creates redundancy since both serve the purpose of having a usable terminal when no specific task context exists.

Current Behavior

In TaskTerminalPanel.tsx:42:

const taskKey = task ? `${task.id}::${task.path}` : 'task-placeholder';

When no task is selected, a placeholder terminal is created. Meanwhile, the global terminal also exists.

Proposed Enhancement

Consider consolidating these so the global terminal serves as the "always available" fallback, and task-specific terminals only exist when there's an actual task selected.

This would:

• Reduce the number of PTY instances
• Simplify the terminal management logic
• Make the architecture more intuitive