GUI fails to launch on Wayland

Since `--socket=x11` was changed to `--socket=fallback-x11` in `finish-args`, the ZAP Flatpak fails to start its GUI on any Wayland session.

### Environment

- ZAP Flatpak `2.17.0` from Flathub
- Manifest commit `ca403f042096` (merge of PR #22), built 2026-07-23
- Flatpak build (OSTree) commit `9da73aa2444a6d8f0e7e3194401aa013b607099b87441ea51ce64237edbe906f`
- Runtime `org.freedesktop.Platform/x86_64/25.08`
- Fedora Linux 44 (KDE Plasma Desktop Edition), Plasma 6.7.4 / KWin 6.7.4, Wayland session

### Steps to reproduce

1. On a Wayland session, install `org.zaproxy.ZAP` from Flathub.
2. Launch it from the desktop icon or run `flatpak run org.zaproxy.ZAP`.

**Expected:** the ZAP GUI opens.
**Actual:** the process exits within a second. `~/.ZAP/zap.log` shows:

```
INFO GuiBootstrap - ZAP 2.17.0 started ... cores: 16 maxMemory: 7 GB
FATAL GuiBootstrap - ZAP GUI is not supported on a headless environment.
Run ZAP inline or in daemon mode, use -help command line argument for more details.
```

### Root cause

`fallback-x11` grants the X11 socket only when Wayland is unavailable. Combined with `--socket=wayland`, a Wayland session therefore gets the Wayland socket and no X11. Inside the sandbox:

```console
$ flatpak run --command=sh org.zaproxy.ZAP -c 'echo "DISPLAY=[$DISPLAY]"; ls /tmp/.X11-unix/'
DISPLAY=[]
(empty)
```

ZAP's UI is Java Swing, and Java 17's AWT has no Wayland backend. With no `DISPLAY`, the JVM reports itself headless and `GuiBootstrap` treats that as fatal.

### Workaround

```console
$ flatpak override --user --socket=x11 org.zaproxy.ZAP
```

This restores normal launch, confirming the socket declaration is the cause.

Start with the Flatpak manifest at the change represented by commit ca403f042096, focusing on its finish-args socket declarations. Reproduce with flatpak run org.zaproxy.ZAP on a Wayland session and inspect DISPLAY and the launch log; done means the ZAP GUI opens without a user override and the headless-environment error no longer occurs.

Written by the indexing model from the issue text.