Bundle PyQtWebEngine on macOS and ship the app as a DMG

pywebview[qt] no longer depends on PyQtWebEngine, so fresh CI builds
produced a macOS app without its Chromium engine that crashed on launch.
Package MediaHive.app as a compressed DMG instead of zipping the raw
onedir folder; release.py accepts .dmg artifacts.

scripts/guibuild.py

@@ -1,5 +1,5 @@
 #!/usr/bin/env -S uv run
-"""Build the desktop GUI application and package it as a version-numbered ZIP.
+"""Build the desktop GUI application and package it as a versioned ZIP/DMG.
 
 Usage:
     uv run scripts/winbuild.py
@@ -13,7 +13,7 @@ This script:
     3. On Windows, downloads the latest ffmpeg.exe for bundling
     4. On macOS arm64, downloads a prebuilt ffmpeg binary for bundling
     4. Builds MediaHive using PyInstaller
-    5. Creates a ZIP file with the version number
+    5. Creates a versioned ZIP (Windows/Linux) or DMG (macOS) artifact
 """
 
 import io
@@ -238,6 +238,33 @@ def create_zip(version: str) -> Path:
     return zip_path
 
 
+def create_dmg(version: str) -> Path:
+    """Create a version-numbered DMG containing MediaHive.app (macOS only)."""
+    repo_root = _REPO_ROOT
+    app_bundle = repo_root / "build" / "MediaHive.app"
+
+    if not app_bundle.exists():
+        raise FileNotFoundError(f"App bundle not found: {app_bundle}")
+
+    dmg_path = repo_root / "build" / f"MediaHive-{version}-{_platform_zip_suffix()}.dmg"
+    dmg_path.parent.mkdir(parents=True, exist_ok=True)
+    dmg_path.unlink(missing_ok=True)
+
+    cmd = [
+        "hdiutil", "create",
+        "-volname", "MediaHive",
+        "-srcfolder", str(app_bundle),
+        "-ov",
+        "-format", "UDZO",
+        str(dmg_path),
+    ]
+    print(f"Running: {' '.join(cmd)}")
+    result = subprocess.run(cmd, cwd=repo_root)
+    if result.returncode != 0:
+        raise RuntimeError(f"hdiutil failed with exit code {result.returncode}")
+    return dmg_path
+
+
 def main() -> None:
     # Windows consoles default to cp1252, which can't encode ✓/✗
     sys.stdout.reconfigure(errors="replace")
@@ -258,10 +285,13 @@ def main() -> None:
             )
         build_wheel()
         build_executable()
-        zip_path = create_zip(version)
+        if sys.platform == "darwin":
+            artifact_path = create_dmg(version)
+        else:
+            artifact_path = create_zip(version)
 
-        print(f"✓ Built successfully: {zip_path}")
-        print(f"  Size: {zip_path.stat().st_size / (1024 * 1024):.1f} MB")
+        print(f"✓ Built successfully: {artifact_path}")
+        print(f"  Size: {artifact_path.stat().st_size / (1024 * 1024):.1f} MB")
     except (FileNotFoundError, OSError, RuntimeError, ValueError) as e:
         print(f"✗ Build failed: {e}", file=sys.stderr)
         sys.exit(1)