ESC key kills ALL background tasks/subagents - poor UX for parallel workflows

Problem

When pressing ESC, it kills all running background tasks and subagents at once. This is problematic for workflows that involve multiple parallel agents.

Current behavior

• User starts multiple background tasks (e.g., 3 ally agents running in parallel)
• User accidentally presses ESC
• All 3 agents are killed immediately

Expected behavior

Either:

1. ESC should only cancel the current foreground operation, not background tasks
2. Or show a confirmation dialog: "You have 3 running tasks. Kill all? [y/N]"
3. Or provide a way to selectively stop tasks (e.g., /tasks stop <id>)

Use case

I frequently run multiple ally agents in parallel for research/review tasks. One accidental ESC destroys all progress.