docs(packaging): add end-to-end Bazzite setup guide

A step-by-step walkthrough for running the host on Bazzite (the immutable
Fedora-Atomic gaming distro): the two install paths (rpm-ostree layering vs the
bootc image), udev + the `input` group, host.env knobs (gamescope-default), the
systemd --user service, firewall ports, verification, and troubleshooting — all
grounded in the packaging/ files. Flags the operator-run COPR, the loopback-only
mgmt port, and that the bundled unit runs the GameStream `serve` host (not m3-host).
Linked from packaging/README.md.

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

packaging/README.md

@@ -4,10 +4,15 @@ The punktfunk host is Linux-only and links system FFmpeg (NVENC), PipeWire, Opus
 the NVIDIA driver. This directory packages it for the **Fedora Atomic / Bazzite** world
 (rpm-ostree + bootc), where most of those deps are already present.
 
+> 👉 **End-to-end Bazzite setup walkthrough** (install → udev/group → `host.env` → service →
+> firewall → verify → troubleshooting): [`bazzite/README.md`](bazzite/README.md). This file is the
+> higher-level packaging rationale.
+
 ```
 packaging/
   rpm/punktfunk.spec      # the RPM (builds punktfunk-host from source with cargo)
   bazzite/host.env        # gamescope-default config for a Bazzite appliance
+  bazzite/README.md       # step-by-step Bazzite setup guide
   bootc/Containerfile     # bake punktfunk into a Bazzite-based atomic image
   copr/                   # COPR build-from-SCM settings
 ```