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_perf_baseline_protocol.py

@@ -21,9 +21,9 @@ SPEC.loader.exec_module(PROTOCOL)
 
 def test_parse_vmrss_kb_reads_kilobytes() -> None:
     """VmRSS lines parse to kilobytes; anything else yields None."""
-    status = "Name:\tvocalinux\nVmRSS:\t  412336 kB\nVmSwap:\t0 kB\n"
+    status = "Name:\tvoculinux\nVmRSS:\t  412336 kB\nVmSwap:\t0 kB\n"
     assert PROTOCOL.parse_vmrss_kb(status) == 412336
-    assert PROTOCOL.parse_vmrss_kb("Name:\tvocalinux\n") is None
+    assert PROTOCOL.parse_vmrss_kb("Name:\tvoculinux\n") is None
 
 
 def test_describe_reports_count_mean_min_max() -> None: