chore(release): drop flatpak, add macOS .dmg, hide Windows console

- .github/workflows/release.yml: remove the build-flatpak job; matrix-
  add macOS (arm64 + x86_64) that builds H7CAD.app by hand, renders
  .icns from assets/logo.svg via librsvg + iconutil, and packages a
  UDZO .dmg. AppImage path updated to packaging/H7CAD.desktop.
- packaging/H7CAD.desktop: moved out of flatpak/ so the AppImage job
  doesn't depend on a Flatpak layout.
- packaging/Info.plist: macOS bundle template; __VERSION__ swapped
  for the release tag at build time.
- flatpak/: deleted (manifests, metainfo, desktop, builder cache).
- src/main.rs: `#![cfg_attr(all(windows, not(debug_assertions)),
  windows_subsystem = "windows")]` so the Windows GUI binary no
  longer spawns a console window alongside it (debug builds keep
  the console for log output).
- README: add macOS install section, document Gatekeeper / SmartScreen
  on first launch since the binaries are unsigned.

Bump to 0.3.5.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -114,7 +114,16 @@ No installation required — runs directly on any modern Linux distribution.
 
 ### Windows
 
-Download `H7CAD.exe` from the [latest release](https://github.com/HakanSeven12/H7CAD/releases/latest) and run it directly.
+Download `H7CAD-*-windows-x86_64.exe` from the [latest release](https://github.com/HakanSeven12/H7CAD/releases/latest) and run it directly. Windows SmartScreen may show "Windows protected your PC" because the binary is not yet code-signed — click **More info → Run anyway**.
+
+### macOS
+
+Download the matching `.dmg` from the [latest release](https://github.com/HakanSeven12/H7CAD/releases/latest):
+
+- Apple Silicon: `H7CAD-*-macos-arm64.dmg`
+- Intel: `H7CAD-*-macos-x86_64.dmg`
+
+Open the .dmg and drag `H7CAD.app` to `/Applications`. The first launch may be blocked by Gatekeeper because the app is not notarised — right-click `H7CAD.app → Open` and confirm, or run once via `xattr -dr com.apple.quarantine /Applications/H7CAD.app`.
 
 ### Build from Source