docs(dist): end-user install front door + serve/pairing/firewall accuracy fixes

Make the host docs match the real distribution path and the actual CLI. Reviewed by a
multi-agent pass (6 editors against one verified fact sheet + an accuracy reviewer); its
findings (a wrong client-Recommends claim, a native-concurrency overstatement) folded in.

- Install front door: new README "Install (host)" method-picker + docs-site/install.md
  (+ nav), routing each distro to its package registry; source build demoted to a fallback.
- Registry-first install: ubuntu-gnome/ubuntu-kde now lead with the apt registry (not a
  cargo build); bazzite leads with the Gitea RPM registry (was COPR/source). Source builds
  moved to an appendix.
- CLI accuracy: serve --native arms pairing from the web console (NOT --allow-pairing, which
  with --require-pairing/--max-concurrent is m3-host-only); --open disables mandatory pairing.
  host-cli/configuration/pairing/quickstart/troubleshooting corrected; mgmt API documented as
  always HTTPS+token. Native host serves one session at a time (extras queue) — not multi.
- Firewall: real ports documented (native UDP 9777 + the ephemeral data port caveat +
  GameStream ports) for Debian + Arch (ufw + nftables), not just Bazzite.
- Sync/accuracy: punktfunk-client (GTK4) presented as a shipping client (not "roadmap"),
  punktfunk-client-rs as the headless tool; host Recommends punktfunk-web only (not the
  client); COPR chroots f43/44; bootc header says Gitea registry not COPR.

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

docs-site/content/docs/meta.json

@@ -4,6 +4,7 @@
     "index",
     "how-it-works",
     "quickstart",
+    "install",
     "---Host Setup---",
     "requirements",
     "ubuntu-gnome",