feat(identity): rename user-visible identity to voculinux with one-time legacy import

The fork takes its own name everywhere a user can see it: binaries
(voculinux, voculinux-gui), desktop entry, autostart, tray, D-Bus
namespace (com.voculinux.Voculinux, no alias for the old name),
config/data/cache dirs, single-instance lock, IBus engine identity,
tray icons, resource prefixes, VOCULINUX_* environment names, and the
update-checker user agent. The internal Python module stays vocalinux
and the distribution metadata keeps the upstream URLs as provenance.

On first run a previous Vocalinux install's config.json, custom
dictionary, and portal restore token are copied once into the new
locations (new config always wins, no merge, no write-back); models
re-resolve through the pinned-checksum download path. An offline
naming-sweep test proves no old-name strings remain on user-visible
surfaces outside the allowlist.

Refs #18

tests/test_recognition_manager_device_config.py

@@ -817,7 +817,7 @@ class TestDownmixToMono(unittest.TestCase):
     def setUpClass(cls):
         # Other test modules may have left sys.modules["numpy"] as MagicMock.
         if isinstance(sys.modules.get("numpy"), MagicMock):
-            real = getattr(sys, "_vocalinux_real_numpy", None)
+            real = getattr(sys, "_voculinux_real_numpy", None)
             if real is not None:
                 sys.modules["numpy"] = real
             else:
@@ -1092,10 +1092,10 @@ class TestVoskInitialization(unittest.TestCase):
         ):
             with patch(
                 "vocalinux.speech_recognition.recognition_manager.SYSTEM_MODELS_DIRS",
-                ["/usr/share/vocalinux"],
+                ["/usr/share/voculinux"],
             ):
                 with patch.object(
-                    manager, "_get_vosk_model_path", return_value="/usr/share/vocalinux/model"
+                    manager, "_get_vosk_model_path", return_value="/usr/share/voculinux/model"
                 ):
                     with patch("os.path.exists", return_value=True):
                         with patch.dict("sys.modules", {"vosk": mock_vosk}):