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

web/package.json

@@ -1,5 +1,5 @@
 {
-  "name": "vocalinux-website",
+  "name": "voculinux-website",
   "version": "0.18.5",
   "private": true,
   "type": "module",
@@ -20,7 +20,7 @@
     "test:all": "npm run test && npm run test:types",
     "test:viewport": "node scripts/viewport-qa.mjs http://127.0.0.1:3456",
     "render:social": "node scripts/render-social-assets.mjs",
-    "deploy": "next build && touch out/.nojekyll && echo 'vocalinux.com' > out/CNAME"
+    "deploy": "next build && touch out/.nojekyll && echo 'voculinux.com' > out/CNAME"
   },
   "dependencies": {
     "@types/node": "^20.14.10",