Trim comments across configs and services

Shorten verbose multi-paragraph comments to essentials, and drop a
stale claim in common.nix that jupiter kept its own copy of the base
config (it now imports common.nix directly).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

services/headscale.nix

@@ -3,14 +3,11 @@
 # Headscale — self-hosted control server for the tailnet. Every host's
 # services/tailscale.nix points --login-server at https://vpn.mgaction.town
 # (this host). MagicDNS base_domain "hosts.mgaction.town" matches the
-# "jupiter.hosts.mgaction.town" style names already used throughout this
-# repo's Caddy vhosts (e.g. hosts/neptun/configuration.nix) — don't change
-# one without the other.
+# "jupiter.hosts.mgaction.town" names used in this repo's Caddy vhosts
+# (e.g. hosts/neptun/configuration.nix) — don't change one without the other.
 #
-# TLS terminates at Caddy (see the host's configuration.nix for the vhost,
-# proxying with `flush_interval -1` since headscale's node-update endpoint
-# is a long-poll and needs unbuffered responses); headscale itself only
-# listens on localhost.
+# TLS terminates at Caddy (see the host's configuration.nix); headscale
+# itself only listens on localhost.
 {
   services.headscale = {
     enable = true;