ci(deb): publish punktfunk-host .deb to the Gitea apt registry

Wires up the half-built Debian packaging: build-deb.sh existed but nothing
invoked or published it. Adds a `deb` workflow that builds the release host in
the Ubuntu 26.04 rust-ci image, packages it (dpkg-shlibdeps-resolved Depends,
NVIDIA driver filtered out), and uploads to Gitea's public Debian registry on
every main push (rolling 0.0.1~ciN.<sha>) and v* tag (clean X.Y.Z). Ubuntu hosts
then track it with `apt update && apt upgrade`.

Also: box-setup docs (packaging/debian/README.md), a pointer from the packaging
README, ignore dist/, and drop backticks from the package Description (the
unquoted control heredoc ran them as a command substitution).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packaging/debian/README.md

@@ -0,0 +1,55 @@
+# punktfunk-host — Debian/Ubuntu package (apt)
+
+`punktfunk-host` is published as a `.deb` to **Gitea's Debian package registry** in the public
+`unom` org, so the Ubuntu hosts update with plain `apt`. CI (`.gitea/workflows/deb.yml`) builds
+and publishes on every push to `main` (a rolling `0.0.1~ciN.<sha>` build) and on `v*` tags
+(a clean `X.Y.Z`).
+
+Package layout mirrors the Fedora RPM (`../rpm/punktfunk.spec`): the host binary, the `/dev/uinput`
+udev rule, the systemd **user** unit, headless session helpers, the example config, and the OpenAPI
+doc. Runtime `Depends` are computed by `dpkg-shlibdeps` from the binary itself (built in the Ubuntu
+26.04 rust-ci image, so the lib soname package names match the target). The NVIDIA driver
+(`libnvidia-encode` / `libEGL_nvidia` / `libcuda`) is **not** a dependency — it's installed out of
+band, like on the RPM side.
+
+## Install on a host (one-time)
+
+The registry is public, so no apt auth is needed — just trust the repo's signing key:
+
+```sh
+sudo install -d -m 0755 /etc/apt/keyrings
+curl -fsSL https://git.unom.io/api/packages/unom/debian/repository.key \
+  | sudo tee /etc/apt/keyrings/punktfunk.asc >/dev/null
+
+echo "deb [signed-by=/etc/apt/keyrings/punktfunk.asc] https://git.unom.io/api/packages/unom/debian stable main" \
+  | sudo tee /etc/apt/sources.list.d/punktfunk.list
+
+sudo apt update
+sudo apt install punktfunk-host
+```
+
+Then, as the desktop user:
+
+```sh
+sudo usermod -aG input "$USER"          # virtual gamepads (re-login to take effect)
+mkdir -p ~/.config/punktfunk
+cp /usr/share/punktfunk-host/host.env.example ~/.config/punktfunk/host.env   # then edit
+systemctl --user enable --now punktfunk-host
+```
+
+## Updates
+
+```sh
+sudo apt update && sudo apt upgrade        # picks up the newest published build
+systemctl --user restart punktfunk-host    # if the unit was already running
+```
+
+## Build a `.deb` locally
+
+```sh
+VERSION=0.0.1 bash packaging/debian/build-deb.sh   # -> dist/punktfunk-host_0.0.1_amd64.deb
+```
+
+Needs `dpkg-dev` (`dpkg-shlibdeps`, `dpkg-deb`). It builds the release binary first if missing.
+Build it in the rust-ci image (or on an Ubuntu 26.04 box) so the resolved `Depends` match the
+hosts; building on a GPU box is fine — the NVIDIA driver lib is filtered out either way.

packaging/debian/build-deb.sh

@@ -123,7 +123,7 @@ Description: Low-latency desktop/game streaming host (Moonlight + punktfunk/1)
  .
  NVENC + GPU EGL come from the NVIDIA driver (libnvidia-encode / libEGL_nvidia),
  installed out of band. After install: add yourself to the 'input' group for virtual
- gamepads, then `systemctl --user enable --now punktfunk-host`.
+ gamepads, then enable the systemd user service punktfunk-host.
 EOF
 
 cat > "$STAGE/DEBIAN/postinst" <<'EOF'