feat(completion): add zstyle verbose option for zsh completion

[vmaerten]

Summary

Add support for the standard Zsh verbose zstyle to customize task completion display.

When users have many tasks, the completion menu can become cluttered with long descriptions. This PR allows users to disable descriptions for a more compact view.

Usage

# Show only task names (no descriptions)
zstyle ':completion:*:*:task:*' verbose false

Why?

The verbose zstyle is the standard Zsh mechanism for controlling description display in completions. It's used by many built-in and third-party completions:

• git - zstyle -T ":completion:${curcontext}:" verbose (https://github.com/zsh-users/zsh/blob/master/Completion/Unix/Command/_git)
• kubectl - supports zstyle ':completion:::kubectl:*' list-grouped false for similar customization (https://kubernetes.io/docs/reference/kubectl/generated/kubectl_completion/)
• Zsh builtins - _directory_stack, _sched, _lp, etc.

By following this convention, Task integrates naturally with users' existing Zsh configurations.

Behavior

Setting	Result
verbose true (default)	build Build the project (aliases: b)
verbose false	build