macOS support (code only, no build yet)

Core.py

@@ -1,11 +1,13 @@
 """Shared app-wide constants: paths, palette, theme.
 
 Paths follow each system's own per-user conventions (no admin needed):
-    Linux                     Windows
-    ~/.config                 %APPDATA%       (settings; roams with the user)
-    ~/.local/share            %LOCALAPPDATA%  (installed programs, SaraSuite's data)
-    ~/.cache                  %LOCALAPPDATA%  (caches, in a Cache/Downloads subfolder)
-so the SaraSuite layout below them (SaraSuite/<Program>/...) is the same on both.
+    Linux            Windows          macOS
+    ~/.config        %APPDATA%        ~/Library/Application Support  (settings)
+    ~/.local/share   %LOCALAPPDATA%   ~/Library/Application Support  (programs, SaraSuite's data)
+    ~/.cache         %LOCALAPPDATA%   ~/Library/Caches               (caches)
+so the SaraSuite layout below them (SaraSuite/<Program>/...) is the same on all
+three. (On macOS settings and data share one folder, as Mac apps' do: the
+programs' config folders and SaraSuite's Programs, Receipts, ... sit side by side.)
 
 The palette and theming mirror SaraFem's Core.py (which mirrors SaraView's),
 and read the same shared ~/.config/SaraSuite/Themes/*.toml files, so a theme
@@ -28,7 +30,10 @@ AppName = "SaraSuite"
 AppVersion = "1.2.5"
 IsFrozen = bool(getattr(sys, "frozen", False))  # running from the AppImage / .exe
 IsWindows = sys.platform == "win32"
-Platform = "Windows" if IsWindows else "Linux"  # matches manifests' Platforms / Platform
+IsMac = sys.platform == "darwin"
+IsLinux = not IsWindows and not IsMac
+# Matches manifests' Platforms / Platform.
+Platform = "Windows" if IsWindows else "macOS" if IsMac else "Linux"
 # Bundled in assets/fonts and always registered, so it works as FontFamily
 # without being installed. Any other FontFamily is looked up among the
 # system's installed fonts.
@@ -44,6 +49,10 @@ if IsWindows:
     # stand-in for a systemd user service).
     StartMenuDir = ConfigHome / "Microsoft" / "Windows" / "Start Menu" / "Programs"
     StartupDir = StartMenuDir / "Startup"
+elif IsMac:
+    ConfigHome = DataHome = Home / "Library" / "Application Support"
+    CacheHome = Home / "Library" / "Caches"
+    StartMenuDir = StartupDir = None
 else:
     ConfigHome = Path(os.environ.get("XDG_CONFIG_HOME") or Home / ".config")
     DataHome = Path(os.environ.get("XDG_DATA_HOME") or Home / ".local" / "share")
@@ -71,8 +80,9 @@ ServicesDir = DataDir / "Services"
 
 # Linux: whether systemd runs the system, and so --user services. Without it
 # (runit on Void, OpenRC, s6, dinit, ...) services run the way they do on
-# Windows (Services.py), started at login from AutostartDir.
-HasSystemd = not IsWindows and Path("/run/systemd/system").is_dir() and shutil.which("systemctl") is not None
+# Windows (Services.py), started at login from AutostartDir. macOS runs them
+# that way too, started at login by a LaunchAgent (MacSupport.py).
+HasSystemd = IsLinux and Path("/run/systemd/system").is_dir() and shutil.which("systemctl") is not None
 AutostartDir = ConfigHome / "autostart"
 
 # Bundled read-only files (program manifests, fonts). Inside a PyInstaller