packaging: add cargo-deb metadata for Debian/Ubuntu .deb builds

Add a [package.metadata.deb] block so the headless default build (no `gui`
feature) — the variant peerspeak spawns as a child — can be packaged with
`cargo deb` from inside a Debian/Ubuntu distrobox. Ships only the pixelpass
binary; runtime shared-lib deps resolved by dpkg-shlibdeps.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Cargo.toml

@@ -6,6 +6,20 @@ description = "P2P screen sharing CLI over iroh"
 license = "MIT OR Apache-2.0"
 publish = false
 
+# Debian/Ubuntu packaging (cargo-deb). Headless default build (no `gui` feature) —
+# that is exactly what peerspeak spawns as a child. Runtime shared-lib deps
+# (libpipewire, libc, …) are resolved by dpkg-shlibdeps via `depends = "$auto"`.
+# Build inside a Debian/Ubuntu distrobox, then `cargo deb --no-build`.
+[package.metadata.deb]
+maintainer = "mollusk <jitty+lc1iz0dc@protonmail.com>"
+section = "net"
+priority = "optional"
+depends = "$auto"
+extended-description = "Peer-to-peer screen sharing over iroh (QUIC). Companion to peerspeak: shares a window or screen directly to a peer with no central server, driven via the CLI and its JSON event stream."
+assets = [
+    ["target/release/pixelpass", "usr/bin/", "755"],
+]
+
 [[bin]]
 name = "pixelpass"
 path = "src/main.rs"