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

snap/local/check_runtime.py

@@ -17,7 +17,7 @@ import runpy
 import sys
 from pathlib import Path
 
-MANIFEST = Path("usr/share/vocalinux/python-inputs.json")
+MANIFEST = Path("usr/share/voculinux/python-inputs.json")
 
 
 def normalize(name: str) -> str:
@@ -80,7 +80,7 @@ def record(root: Path, source: Path) -> None:
         if importlib.metadata.version(name) != expected_version:
             raise RuntimeError(f"Build tool {name} differs from its locked version")
     expected = locked_versions(source / "requirements/runtime.txt")
-    expected["vocalinux"] = runpy.run_path(str(source / "src/vocalinux/version.py"))["__version__"]
+    expected["voculinux"] = runpy.run_path(str(source / "src/vocalinux/version.py"))["__version__"]
     audit(root, expected)
     manifest = {
         "python": list(sys.version_info[:2]),