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

packaging/appimage/native-cache.sh

@@ -12,7 +12,7 @@ _NATIVE_CACHE_HERE="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 pywhispercpp_native_cache_dir() {
     local arch="$1"
     local root id
-    root="${VOCALINUX_APPIMAGE_CACHE:-${XDG_CACHE_HOME:-$HOME/.cache}/vocalinux-appimage}"
+    root="${VOCULINUX_APPIMAGE_CACHE:-${XDG_CACHE_HOME:-$HOME/.cache}/voculinux-appimage}"
     id="$(bash "$_NATIVE_CACHE_HERE/native-cache-id.sh")"
     printf '%s\n' "$root/pywhispercpp-vulkan-${arch}-${id}"
 }
@@ -26,7 +26,7 @@ pywhispercpp_cache_has_vulkan() {
 }
 
 # Copy the pywhispercpp install out of a site-packages directory.
-# Leaves the rest of the prefix (Vocalinux, numpy, …) where it is.
+# Leaves the rest of the prefix (Voculinux, numpy, …) where it is.
 pywhispercpp_cache_publish() {
     local site="$1" dest="$2"
     local parent staging pattern backup