fix(packaging): correct CachyOS firewall to ufw + ship ufw openers + web-console opener

CachyOS ships ufw enabled by default (firewalld is not installed) — verified live
on the .21 box — but the docs and shipped firewall openers claimed "CachyOS enables
firewalld by default". Correct that everywhere and ship a ufw application profile
(the one-liner analogue of the firewalld service files):

- packaging/linux/punktfunk.ufw (new): [punktfunk-native], [punktfunk-gamestream],
  [punktfunk-web] profiles, installed to /etc/ufw/applications.d/punktfunk by the
  Arch (CachyOS) and .deb host packages. `sudo ufw allow punktfunk-native`.
- packaging/linux/punktfunk-web.xml (new): firewalld service for the optional web
  console (TCP 47992), installed by the host package on arch/deb/rpm. Neither the
  native nor gamestream opener covered 47992, so a firewalld/ufw host that enabled
  punktfunk-web could not reach the console over the LAN.
- Fix the "CachyOS enables firewalld" claim in arch.md, arch/README.md,
  debian/README.md, both firewalld service .xml comments, and the pacman scriptlet;
  firewalld now attributed to the spins that use it (EndeavourOS, Fedora/RHEL).
- Docs present both one-liners (ufw + firewalld) whichever firewall you run, plus a
  console-opener step; postinst/scriptlet hints detect ufw as well as firewalld.

The native data plane stays hole-punched (ephemeral UDP, no fixed port) — its
openers correctly open only 9777/udp + mDNS; the stale "open a UDP range" note is
replaced with the accurate outbound-UDP explanation.

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

packaging/linux/punktfunk-web.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  firewalld service definition for the punktfunk management web console (the optional punktfunk-web
+  package: device pairing, status, GPU selection, performance graphs).
+
+  Installed to /usr/lib/firewalld/services/ by the punktfunk-host package. NOT enabled automatically
+  (packages never touch the admin's firewall). Only useful if you installed the console (punktfunk-web)
+  AND want to reach it from another device on the LAN — the console binds all interfaces on TCP 47992
+  (HTTPS, login-gated). The streaming host itself does not need this open; enable it deliberately with
+  firewall-cmd (add-service=punktfunk-web, then reload). CachyOS/Ubuntu: use the ufw punktfunk-web
+  profile instead.
+
+  The mgmt REST API (TCP 47990) is a different, loopback-only surface (the console proxies to it
+  locally) and is deliberately NOT opened here.
+-->
+<service>
+  <short>Punktfunk web console</short>
+  <description>The optional punktfunk management web console (device pairing, status, GPU selection, performance graphs) over HTTPS. Open only if you run the punktfunk-web package and want the console reachable from other devices on the LAN.</description>
+  <port protocol="tcp" port="47992"/>  <!-- HTTPS web console (login-gated) -->
+</service>