## What happened

Running `ga <branch>` for a branch that already exists prints a fatal error — and then moves you into the existing worktree anyway, as though it had succeeded. `mise trust` also runs on the path that was not created.

## Cause

In `default/bash/fns/worktrees`, `ga()` does not check the result of the add:

```bash
git worktree add -b "$branch" "$wt_path"
mise trust "$wt_path"
cd "$wt_path"
```

When the branch already exists, `git worktree add` fails but `$wt_path` is still the path of the worktree created by the *earlier* successful `ga`, so the `cd` succeeds. The error message and the shell's behaviour disagree.

## What was expected

A failed `git worktree add` aborts, leaving the shell where it was.

## Steps to reproduce

```bash
cd some-repo
ga feature-x            # succeeds, moves you to ../some-repo--feature-x
cd ../some-repo
ga feature-x
# fatal: a branch named 'feature-x' already exists
pwd
# .../some-repo--feature-x   <- moved anyway, despite the fatal error
```

Verified with `mise` stubbed: `mise trust ../some-repo--feature-x` is still called on the failing run.

## Fix

```bash
git worktree add -b "$branch" "$wt_path" || return 1
mise trust "$wt_path"
cd "$wt_path"
```

## System

- Omarchy 4.0.1-1
- `/usr/share/omarchy/default/bash/fns/worktrees`, lines 11-13