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_capture_shutdown.py

@@ -26,7 +26,7 @@ def manager(monkeypatch: pytest.MonkeyPatch) -> Generator[rm.SpeechRecognitionMa
     monkeypatch.setattr(rm.SpeechRecognitionManager, "_init_vosk", lambda self: None)
     monkeypatch.setattr(rm, "load_silero_vad", lambda: None)
     monkeypatch.setattr(rm.SpeechRecognitionManager, "_download_selected_model_if_missing", Mock())
-    monkeypatch.setitem(sys.modules, "numpy", sys._vocalinux_real_numpy)
+    monkeypatch.setitem(sys.modules, "numpy", sys._voculinux_real_numpy)
     for name in ("play_start_sound", "play_stop_sound", "play_error_sound"):
         monkeypatch.setattr(rm, name, Mock())
     monkeypatch.setattr(rm, "_CAPTURE_JOIN_SECONDS", 0.02)