"Unable to parse configuration file" is not a helpful error message

If I upload an invalid configuration file and run `makoctl reload`, I get this:

```
Unable to parse configuration file (fr.emersion.Mako.InvalidConfig)
```

which is not very helpful. It would be more useful if it could at least give the line number where it had the problem.

## To reproduce

Set this as the Mako config and run `makoctl reload`

```ini
[app-name=niri summary=Screenshot captured]
history=0
default-timeout=3000
ignore-timeout=1
```

It would be more helpful to indicate that the error is in line 1 — and even more helpful if it could add something like `Invalid criterion "captured"`, which would give me the clue that I'd forgotten to put quotes around the summary.