Add a Mac as the third system, beside Wayland and X11

Dikte already chose its clipboard programs once instead of in every
function; macOS joins that table rather than adding a branch to each one.
A Mac copies through pbcopy and presses Cmd+V straight into CoreGraphics,
records through AVFoundation, and asks Carbon for its global shortcuts.

The three tables are paste.Desktop, audio.Sound, and the pair of
predicates in hotkey.py. Each reads sys.platform inside the chooser, so a
test can stand somewhere else: 697 of the 737 tests now run on any
machine, the Wayland and X11 halves included, and the suite passes whole
whichever system it is run on.

Two things a Mac does not have needed saying rather than pretending:
there is no shortcut registry to install into, so Settings offers no
Install button and the listener is the mechanism instead of a fallback;
and nothing is offered as the sound the speakers are playing, so a
meeting needs BlackHole or Loopback and says so. The KDE-only labels
around them were already wrong on GNOME, and now name whichever desktop
is there.

Co-authored-by: firat <[email protected]>

tests/__init__.py

@@ -17,6 +17,11 @@ os.environ.setdefault("QT_QPA_PLATFORM", "offscreen")
 _SANDBOX = tempfile.mkdtemp(prefix="dikte-tests-")
 os.environ["XDG_CONFIG_HOME"] = os.path.join(_SANDBOX, "config")
 os.environ["XDG_DATA_HOME"] = os.path.join(_SANDBOX, "data")
+# Home goes with them: the shortcut file, the applications directory and every
+# macOS path start from it rather than from an XDG variable, and a test run is
+# not allowed to touch the real one.
+os.environ["HOME"] = os.path.join(_SANDBOX, "home")
+os.makedirs(os.environ["HOME"], exist_ok=True)
 atexit.register(shutil.rmtree, _SANDBOX, True)
 
 # A key sitting in the environment would otherwise reach the code that falls