Add Void Linux packaging; fix production builds embedding the frontend

Voiced now ships as a native Void Linux package:
- packaging/void/template: xbps-src template
- packaging/void/build-xbps.sh: builds and indexes a local .xbps repository
- packaging/void/voiced.desktop: application entry

Also fixes a real bug: the `custom-protocol` feature was never enabled, so
releases ran in development mode and tried to reach a dev server on
localhost:1420 instead of serving the embedded frontend. It is now declared
in Cargo.toml and passed explicitly by every build script.

The Void package output moved out of Vite's `dist/` (which is wiped on each
build) to `build/void/`.

Co-authored-by: CommandCodeBot <noreply@commandcode.ai>

README.md

@@ -90,6 +90,35 @@ distributions that don't package NSIS (e.g. Void Linux):
 With those in place, `npm run app:build:windows` produces the NSIS `-setup.exe` and the
 portable `voiced.exe`.
 
+## Installing on Void Linux
+
+Two ways to get a native `.xbps` package.
+
+### Prebuilt binary package (no xbps-src needed)
+
+```bash
+./packaging/void/build-xbps.sh          # -> build/void/repo/voiced-<version>_1.<arch>.xbps
+echo "repository=$(pwd)/build/void/repo" | sudo tee /etc/xbps.d/99-voiced-local.conf
+sudo xbps-install -Sy voiced
+```
+
+Launch **Voiced** from the application menu, or run `voiced`. Remove it with
+`sudo xbps-remove voiced`.
+
+The package installs `/usr/bin/voiced`, a desktop entry and hicolor icons, and depends on
+`libwebkit2gtk41`.
+
+### Building through xbps-src
+
+Copy `packaging/void/template` into a `void-packages` checkout and build it the standard way:
+
+```bash
+cp -r packaging/void/template void-packages/srcpkgs/voiced/template
+cd void-packages && ./xbps-src pkg voiced
+```
+
+See the comments at the top of the template about the private source archive and checksums.
+
 ## Where data lives
 
 | What                | Location                                                       |
@@ -108,6 +137,7 @@ src/                 React + Carbon frontend
 src-tauri/           Rust backend (Tauri commands, SQLite schema, asset store)
 public/brand/        Bongbetic + vendor brand assets
 public/fonts/        IBM Plex (woff/woff2)
+packaging/void/      Void Linux packaging (xbps-src template + build script + desktop entry)
 ```
 
 ## Ownership