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

justfile

@@ -1,4 +1,4 @@
-# Vocalinux justfile
+# Voculinux justfile
 # Convenient commands for development
 # Run `just` to list all recipes. Python tooling runs through `uv run` against
 # .venv/ — run `just deps` after cloning (requires uv).
@@ -47,7 +47,7 @@ _check_build_deps:
 _tooling: _check_build_deps
     uv sync --inexact {{DEV_EXTRAS}}
 
-# Install Vocalinux
+# Install Voculinux
 install:
     ./install.sh
 
@@ -149,7 +149,7 @@ aur-gate:
     uv pip install --no-config --python "$WORK/venv/bin/python" \
       --require-hashes --no-deps --only-binary=:all: -r requirements/release-build.txt
     "$WORK/venv/bin/python" scripts/prepare_aur_source.py \
-      --local-unattested --sdist "$WORK"/dist/vocalinux-*.tar.gz --output "$WORK/source"
+      --local-unattested --sdist "$WORK"/dist/voculinux-*.tar.gz --output "$WORK/source"
     docker run --rm -v "$PWD:/repo:ro" -v "$WORK/source:/aur-source:ro" \
       -e AUR_SOURCE=/aur-source archlinux:latest bash /repo/packaging/aur/build-test.sh
 
@@ -294,11 +294,11 @@ clean:
 
 # Run the installed application
 run:
-    vocalinux
+    voculinux
 
 # Run the installed application with debug logging
 run-debug:
-    vocalinux --debug
+    voculinux --debug
 
 # Run from source
 run-source: _tooling
@@ -314,4 +314,4 @@ pre-commit: _tooling
 
 # Print the current version
 version:
-    @uv run --no-sync python -c "from src.vocalinux.version import __version__; print(__version__)"
+    @uv run --no-sync python -c "from src.voculinux.version import __version__; print(__version__)"