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_config_manager.py

@@ -32,7 +32,7 @@ class TestConfigManager(unittest.TestCase):
         """Set up test environment."""
         # Create a temporary directory for configuration
         self.temp_dir = tempfile.TemporaryDirectory()
-        self.temp_config_dir = os.path.join(self.temp_dir.name, ".config/vocalinux")
+        self.temp_config_dir = os.path.join(self.temp_dir.name, ".config/voculinux")
         _ensure_test_config_dir(self.temp_config_dir)
         self.temp_config_file = os.path.join(self.temp_config_dir, "config.json")
 
@@ -891,7 +891,7 @@ class TestTypedAccessors(unittest.TestCase):
     def test_whispercpp_advanced_persistence(self):
         # This class skips ConfigManager.__init__, so unlike TestConfigManager
         # nothing has redirected CONFIG_FILE: without the patches below this
-        # save_config() overwrites the developer's real ~/.config/vocalinux/
+        # save_config() overwrites the developer's real ~/.config/voculinux/
         # config.json with the synthetic fixture from setUp.
         with tempfile.TemporaryDirectory() as temp_dir:
             temp_file = os.path.join(temp_dir, "config.json")