Initial scaffold: README, distcc-avahi PKGBUILD, CI stub

- README documents repo layout, client setup (Arch+Debian),
  signing-key fingerprint, and infra TODOs.
- arch/distcc-avahi/: ALARM distcc PKGBUILD with --with-avahi,
  avahi dep, distccd.service + conf.d + tmpfiles.
- .gitea/workflows/build.yml: placeholder with wiring sketch
  for the real pipeline (runners, signing, scp publish).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

arch/distcc-avahi/distccd.service

@@ -0,0 +1,15 @@
+[Unit]
+Description=distcc compile server (Zeroconf-announced)
+After=network-online.target avahi-daemon.service
+Wants=network-online.target avahi-daemon.service
+
+[Service]
+Type=simple
+EnvironmentFile=/etc/conf.d/distccd
+User=nobody
+Group=nobody
+ExecStart=/usr/bin/distccd --no-detach --daemon $DISTCC_OPTS
+Restart=on-failure
+
+[Install]
+WantedBy=multi-user.target