fix(flatpak): move runtime to KDE 6.10 (freedesktop 25.08)

Restore the Flatpak manifest to the repo and target org.kde.Platform
6.10 instead of the EOL 6.6/23.08 stack reported in issue #5.

Add a maintainer build script and a CI job that verifies the manifest
builds against the current KDE SDK.

de.nerdbear.bearwave.json

@@ -0,0 +1,34 @@
+{
+    "app-id": "de.nerdbear.bearwave",
+    "runtime": "org.kde.Platform",
+    "runtime-version": "6.10",
+    "sdk": "org.kde.Sdk",
+    "command": "bearwave",
+    "finish-args": [
+        "--share=network",
+        "--socket=wayland",
+        "--socket=fallback-x11",
+        "--socket=pulseaudio",
+        "--own-name=org.mpris.MediaPlayer2.bearwave",
+        "--talk-name=org.freedesktop.Notifications",
+        "--talk-name=org.kde.StatusNotifierWatcher",
+        "--share=ipc"
+    ],
+    "modules": [
+        {
+            "name": "bearwave",
+            "buildsystem": "cmake-ninja",
+            "builddir": true,
+            "config-opts": [
+                "-DCMAKE_BUILD_TYPE=Release",
+                "-DBEARWAVE_BUILD_TESTS=OFF"
+            ],
+            "sources": [
+                {
+                    "type": "dir",
+                    "path": "."
+                }
+            ]
+        }
+    ]
+}