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

CONTRIBUTING.md

@@ -1,4 +1,4 @@
-# Contributing to Vocalinux
+# Contributing to Voculinux
 
 Thanks for your interest in contributing. This guide covers setup, style, testing, and pull requests.
 
@@ -18,8 +18,8 @@ Participation is covered by our [Code of Conduct](CODE_OF_CONDUCT.md). Be respec
 ### Automated (recommended)
 
 ```bash
-git clone https://github.com/YOUR-USERNAME/vocalinux.git
-cd vocalinux
+git clone https://github.com/YOUR-USERNAME/voculinux.git
+cd voculinux
 ./install.sh --dev
 ```
 
@@ -152,7 +152,7 @@ just typecheck # mypy src/
 ### Project structure
 
 ```
-vocalinux/
+voculinux/
 ├── src/vocalinux/            # Application
 │   ├── main.py
 │   ├── speech_recognition/   # Engines + command processor