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

flake.nix

@@ -1,5 +1,5 @@
 {
-  description = "Vocalinux — free, offline voice dictation for Linux";
+  description = "Voculinux — free, offline voice dictation for Linux";
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
@@ -21,40 +21,40 @@
           pkgs = nixpkgs.legacyPackages.${system};
         in
         {
-          vocalinux = pkgs.python3Packages.callPackage ./packaging/nix/package.nix {
+          voculinux = pkgs.python3Packages.callPackage ./packaging/nix/package.nix {
             pywhispercpp = pkgs.python3Packages.callPackage ./packaging/nix/pywhispercpp.nix { };
             src = self;
           };
-          default = self.packages.${system}.vocalinux;
+          default = self.packages.${system}.voculinux;
         }
       );
 
       apps = forAllSystems (system: {
-        vocalinux = {
+        voculinux = {
           type = "app";
-          program = "${self.packages.${system}.vocalinux}/bin/vocalinux";
+          program = "${self.packages.${system}.voculinux}/bin/voculinux";
         };
-        default = self.apps.${system}.vocalinux;
+        default = self.apps.${system}.voculinux;
       });
 
       overlays.default = final: prev: {
-        vocalinux = self.packages.${prev.stdenv.hostPlatform.system}.vocalinux;
+        voculinux = self.packages.${prev.stdenv.hostPlatform.system}.voculinux;
       };
 
-      nixosModules.vocalinux =
+      nixosModules.voculinux =
         { pkgs, lib, ... }:
         {
           imports = [ ./packaging/nix/module.nix ];
-          programs.vocalinux.package = lib.mkDefault self.packages.${pkgs.stdenv.hostPlatform.system}.vocalinux;
+          programs.voculinux.package = lib.mkDefault self.packages.${pkgs.stdenv.hostPlatform.system}.voculinux;
         };
-      nixosModules.default = self.nixosModules.vocalinux;
+      nixosModules.default = self.nixosModules.voculinux;
 
-      homeManagerModules.vocalinux =
+      homeManagerModules.voculinux =
         { pkgs, lib, ... }:
         {
           imports = [ ./packaging/nix/home-manager.nix ];
-          programs.vocalinux.package = lib.mkDefault self.packages.${pkgs.stdenv.hostPlatform.system}.vocalinux;
+          programs.voculinux.package = lib.mkDefault self.packages.${pkgs.stdenv.hostPlatform.system}.voculinux;
         };
-      homeManagerModules.default = self.homeManagerModules.vocalinux;
+      homeManagerModules.default = self.homeManagerModules.voculinux;
     };
 }