Add separate delete options: workflow+branch, workflow only, branch only

[nsheaps]

Description

Provide separate delete options for more granular control:

1. Delete worktree + branch - Current behavior, removes both
2. Delete worktree only - Remove the worktree but keep the branch
3. Delete branch only - Available when not on a worktree, removes just the branch

Use Cases

• Keep branch for later work while cleaning up disk space (worktree only)
• Clean up merged branches without worktrees (branch only)
• Full cleanup when done with feature (both)

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CLI / Non-TTY Mode Context

When running in non-interactive (non-TTY) environments or via CLI arguments, delete behavior changes:

CLI Usage

git-wt d <branch>      # Delete worktree+branch (requires --force in non-interactive)
git-wt d <branch> --force  # Force delete without confirmation

Behavior

• Interactive mode: Shows gum confirmation prompt before deletion
• Non-interactive mode: Requires --force flag, otherwise fails with error
• If branch has no worktree, git-wt d fails with an error

Related to Non-TTY Mode

The delete command is part of the broader CLI argument support:

• git-wt [branch] - Switch to/create worktree (prints path by default)
• git-wt d [branch] - Delete worktree+branch
• --exec flag spawns new shell instead of just printing path
• --force flag for non-interactive deletion