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_release_integrity.py

@@ -249,7 +249,7 @@ def test_flatpak_release_jobs_reuse_ci_builder_pins():
             "action's restore-keys prefix matches after it appends -${arch}"
         )
         assert f"runs-on: {runner}" in block
-        assert f"Vocalinux-${{{{ steps.get_version.outputs.VERSION }}}}-{arch}.flatpak" in block
+        assert f"Voculinux-${{{{ steps.get_version.outputs.VERSION }}}}-{arch}.flatpak" in block
         assert "actions/upload-artifact" in block, f"{name} does not upload a workflow artifact"
         assert "gh release upload" not in block, f"{name} cannot run gh in the builder image"
         assert "python -m build" not in _without_comments(block)
@@ -273,7 +273,7 @@ def test_the_release_notes_document_flatpak_bundles():
     assert "org.gnome.Platform//50" in body
     assert "no auto-update" in body
     assert "not on Flathub" in body
-    assert "Vocalinux-__VERSION__-x86_64.flatpak" in body
+    assert "Voculinux-__VERSION__-x86_64.flatpak" in body
 
 
 def test_the_remote_install_guidance_only_runs_when_the_remote_publishes():