Add an `ask` attribute to commands that shows a y/n confirmation
before executing. If the user declines, the command is skipped but
the task continues with the next command.

Example:
```yaml
cmds:
  - cmd: echo "Deploying..."
    ask: "Deploy to production?"
  - task: run-migrations
    ask: "Run database migrations?"
```

Behavior:
- Default: asks for y/n confirmation
- --yes: auto-confirms all asks
- --dry: shows commands without asking

This differs from task-level `prompt:` which cancels the entire task
if declined. Command-level `ask:` only skips the individual command.