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_ibus_engine_utils.py

@@ -10,7 +10,7 @@ import sys
 import unittest
 from unittest.mock import MagicMock, patch
 
-# Mock GI imports before importing any vocalinux modules that use gi.
+# Mock GI imports before importing any voculinux modules that use gi.
 # On CI, real gi/IBus may be installed; importing ibus_engine without mocks
 # would set IBUS_AVAILABLE=True and VocalinuxEngine would inherit from real
 # IBus.Engine, causing hangs when super().__init__() tries to connect to IBus.
@@ -31,7 +31,7 @@ sys.modules["gi.repository"] = _mock_gi_repo
 
 # Force reload ibus_engine so it picks up mocks (in case it was already imported)
 for _key in list(sys.modules.keys()):
-    if "vocalinux" in _key and "ibus_engine" in _key:
+    if "voculinux" in _key and "ibus_engine" in _key:
         del sys.modules[_key]
 
 
@@ -323,8 +323,8 @@ class TestSwitchEngine(unittest.TestCase):
         """Test successfully switching engines."""
         from vocalinux.text_injection.ibus_engine import switch_engine
 
-        mock_get_engine.return_value = "vocalinux"
-        result = switch_engine("vocalinux")
+        mock_get_engine.return_value = "voculinux"
+        result = switch_engine("voculinux")
         self.assertTrue(result)
 
     @patch("vocalinux.text_injection.ibus_engine.get_current_engine")
@@ -335,7 +335,7 @@ class TestSwitchEngine(unittest.TestCase):
         from vocalinux.text_injection.ibus_engine import switch_engine
 
         mock_get_engine.return_value = "other"
-        result = switch_engine("vocalinux")
+        result = switch_engine("voculinux")
         self.assertFalse(result)
 
 
@@ -381,7 +381,7 @@ class TestStopEngineProcess(unittest.TestCase):
 
         cmdline = MagicMock()
         cmdline.exists.return_value = True
-        cmdline.read_text.return_value = "python /x/vocalinux/text_injection/ibus_engine.py --ibus"
+        cmdline.read_text.return_value = "python /x/voculinux/text_injection/ibus_engine.py --ibus"
         mock_path_cls.return_value = cmdline
 
         # SIGTERM succeeds; first liveness check still alive; second gone.
@@ -409,7 +409,7 @@ class TestStopEngineProcess(unittest.TestCase):
 
         cmdline = MagicMock()
         cmdline.exists.return_value = True
-        cmdline.read_text.return_value = "python /x/vocalinux/text_injection/ibus_engine.py --ibus"
+        cmdline.read_text.return_value = "python /x/voculinux/text_injection/ibus_engine.py --ibus"
         mock_path_cls.return_value = cmdline
 
         # SIGTERM, then keep reporting alive until wait timeout, then SIGKILL succeeds.