Vector subtraction in `look_at` inverts the forward vector

**Bevy version**

0.4.0

**Operating system & version**

Linux

**What you did**

Calling `forward` on a `Transform` created by `look_at` gives the result in what appears to be the wrong direction.

**What you expected to happen**

I was expecting `forward` called on a `Transform` (for a `Camera`) created by `look_at` to be pointing towards the target.

**What actually happened**

It was pointing backwards.

**Additional information**

The code of `look_at` looks like:
`let forward = Vec3::normalize(self.translation - target);`

This means the vector `forward` will go from `target` to `self.translation`, so in reality it will be pointing backward from the `target`, instead of forward...

Are we in some Camera-local coordinate system here, with the directions inverted? Maybe I'm just confused...

Start by inspecting the Transform::look_at implementation and the forward call described in the report. Verify the engine's camera-local direction convention and whether the subtraction matches the documented target-facing behavior; done means the reported direction is consistent and the behavior is covered by an appropriate regression check.

Written by the indexing model from the issue text.