[client/ui] Fix Linux package metadata and KDE Wayland icon association

Two Linux packaging issues, both surfaced by the netbird-ui deb/rpm
built from .goreleaser_ui.yaml.

1) License / vendor metadata
----------------------------
The nfpm entries for the UI package set only maintainer/description/
homepage, leaving the License and Vendor RPM/DEB tags empty. KDE
Discover (and GNOME Software) then render the package as
"Licenses: Unknown" / "Unknown author", with a scary license-warning
popup on install. The daemon's main .goreleaser.yaml already set
license (commit #5659) but never vendor, and the UI config was skipped
entirely.

Fix: add `license: BSD-3-Clause` + `vendor: NetBird` to both UI nfpm
entries (deb + rpm), and `vendor: NetBird` to the daemon's deb + rpm
entries for consistency. BSD-3-Clause is correct for client/ui — the
repo is BSD-3-Clause except management/, signal/, relay/, combined/
(AGPLv3), none of which the UI touches.

2) KDE Wayland window/taskbar icon
----------------------------------
On KDE Plasma 6 under Wayland the app launched with the generic Wails
icon in the window titlebar and the taskbar / Alt-Tab switcher, even
though /usr/share/pixmaps/netbird.png (the launcher icon, resolved from
the desktop entry's `Icon=netbird`) was correct.

Root cause is how a Wayland compositor decides a window's icon. Unlike
X11 there is no per-window _NET_WM_ICON the app can push at runtime —
GTK4 even removed gtk_window_set_icon, so the embedded assets/netbird.png
the binary carries is simply ignored. Instead the compositor matches the
window's Wayland **app_id** to an installed .desktop file and uses that
entry's `Icon=` key.

The app_id is not "netbird": Wails hardcodes it as `org.wails.<name>`
(pkg/application/linux_cgo.go: `fmt.Sprintf("org.wails.%s", name)`, name
= sanitized Options.Name), yielding **org.wails.netbird**. There is no
Wails option to override the prefix. Verified the live value on the
Fedora-40 / KDE 6.3 / Wayland test VM by dumping workspace.windowList()
via a KWin script:

    js: ZZZWIN org.wails.netbird ## NetBird

KDE needs two things to associate the running window with our desktop
entry and thus paint our icon:
  - the desktop entry's basename should equal the app_id, so the
    titlebar decoration (which looks the entry up by app_id ->
    <app_id>.desktop) finds it, and
  - a `StartupWMClass=<app_id>` line, which the taskbar / task switcher
    use to map the surface to the entry.

Fix (no Wails fork needed — app_id stays org.wails.netbird, which the
user never sees; only Name=NetBird and the icon are visible):
  - install the desktop file as `org.wails.netbird.desktop` instead of
    `netbird.desktop` (both deb and rpm contents in .goreleaser_ui.yaml)
  - add `StartupWMClass=org.wails.netbird` to
    client/ui/build/linux/netbird.desktop

`Icon=netbird` and the pixmaps/netbird.png payload are unchanged — they
were already correct. Confirmed on the test VM that both the titlebar
and taskbar/Alt-Tab now show the NetBird icon.

.goreleaser.yaml

@@ -196,6 +196,7 @@ nfpms:
     description: Netbird client.
     homepage: https://netbird.io/
     license: BSD-3-Clause
+    vendor: NetBird
     id: netbird_deb
     bindir: /usr/bin
     builds:
@@ -210,6 +211,7 @@ nfpms:
     description: Netbird client.
     homepage: https://netbird.io/
     license: BSD-3-Clause
+    vendor: NetBird
     id: netbird_rpm
     bindir: /usr/bin
     builds:

.goreleaser_ui.yaml

@@ -70,6 +70,8 @@ nfpms:
   - maintainer: Netbird <dev@netbird.io>
     description: Netbird client UI.
     homepage: https://netbird.io/
+    license: BSD-3-Clause
+    vendor: NetBird
     id: netbird_ui_deb
     package_name: netbird-ui
     builds:
@@ -80,7 +82,7 @@ nfpms:
       postinstall: "release_files/ui-post-install.sh"
     contents:
       - src: client/ui/build/linux/netbird.desktop
-        dst: /usr/share/applications/netbird.desktop
+        dst: /usr/share/applications/org.wails.netbird.desktop
       - src: client/ui/build/appicon.png
         dst: /usr/share/pixmaps/netbird.png
     dependencies:
@@ -92,6 +94,8 @@ nfpms:
   - maintainer: Netbird <dev@netbird.io>
     description: Netbird client UI.
     homepage: https://netbird.io/
+    license: BSD-3-Clause
+    vendor: NetBird
     id: netbird_ui_rpm
     package_name: netbird-ui
     builds:
@@ -102,7 +106,7 @@ nfpms:
       postinstall: "release_files/ui-post-install.sh"
     contents:
       - src: client/ui/build/linux/netbird.desktop
-        dst: /usr/share/applications/netbird.desktop
+        dst: /usr/share/applications/org.wails.netbird.desktop
       - src: client/ui/build/appicon.png
         dst: /usr/share/pixmaps/netbird.png
     dependencies:

client/ui/build/linux/netbird.desktop

@@ -5,4 +5,5 @@ Icon=netbird
 Type=Application
 Terminal=false
 Categories=Utility;
-Keywords=netbird;
+Keywords=netbird;
+StartupWMClass=org.wails.netbird