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_cancellation.py

@@ -116,7 +116,7 @@ def test_overflow_does_not_reset_deadline(stream: MagicMock, clock: SimpleNamesp
 def test_portaudio_chunk_preserves_normalization(
     stream: MagicMock, monkeypatch: pytest.MonkeyPatch
 ) -> None:
-    monkeypatch.setitem(sys.modules, "numpy", sys._vocalinux_real_numpy)
+    monkeypatch.setitem(sys.modules, "numpy", sys._voculinux_real_numpy)
     stream.read.return_value = b"\x64\x00\x64\x00" * 1024
     source = capture.PortAudioCaptureSource()
     source.stream = stream
@@ -133,7 +133,7 @@ def audio_test(monkeypatch: pytest.MonkeyPatch, stream: MagicMock) -> tuple[Magi
     """Supply one negotiated stream without touching PortAudio or the desktop."""
     audio = MagicMock()
     audio.get_default_input_device_info.return_value = {"name": "Test Mic", "index": 3}
-    monkeypatch.setitem(sys.modules, "numpy", sys._vocalinux_real_numpy)
+    monkeypatch.setitem(sys.modules, "numpy", sys._voculinux_real_numpy)
     monkeypatch.setitem(sys.modules, "pyaudio", MagicMock(PyAudio=lambda: audio, paInt16=8))
     monkeypatch.setattr(capture, "_open_capture_stream", lambda *_args: (1, 16000, stream))
     return audio, stream
@@ -246,7 +246,7 @@ def test_pipewire_select_is_sliced_and_cancellable(monkeypatch: pytest.MonkeyPat
 def test_pipewire_test_partial_failure_cleans_up(
     monkeypatch: pytest.MonkeyPatch, failure: str
 ) -> None:
-    monkeypatch.setitem(sys.modules, "numpy", sys._vocalinux_real_numpy)
+    monkeypatch.setitem(sys.modules, "numpy", sys._voculinux_real_numpy)
     source = MagicMock(sample_rate=16000, _CHUNK_FRAMES=1024)
     source.read_chunk.side_effect = [
         b"\x01\x00" * 1024,