Add etc/ source tree for package-shipped /etc files

This tree is the source for omarchy-settings to install into /etc
(for paths Omarchy fully owns) or stage at /usr/share/omarchy/etc-overrides
(for paths upstream packages own, which the post_install copies into place).

Package-owned drop-ins (no upstream conflict):
- etc/docker/daemon.json
- etc/systemd/system/docker.service.d/no-block-boot.conf
- etc/systemd/resolved.conf.d/20-docker-dns.conf
- etc/systemd/resolved.conf.d/10-disable-multicast.conf
- etc/systemd/system.conf.d/10-faster-shutdown.conf
- etc/systemd/system/user@.service.d/10-faster-shutdown.conf
  (renamed from .../faster-shutdown.conf for consistency)
- etc/systemd/logind.conf.d/10-ignore-power-button.conf
  (replaces the previous in-place sed-edit of logind.conf)
- etc/gnupg/dirmngr.conf
- etc/sysctl.d/99-omarchy-sysctl.conf  (renamed from the 99-sysctl.conf
  appendage; a migration cleans up the old path on existing installs)
- etc/sysctl.d/90-omarchy-file-watchers.conf
- etc/modprobe.d/omarchy-usb-autosuspend.conf
  (renamed from disable-usb-autosuspend.conf)
- etc/sudoers.d/omarchy-asdcontrol
  (renamed from asdcontrol; $USER -> %wheel for packaging)
- etc/sudoers.d/omarchy-tzupdate
- etc/sudoers.d/omarchy-passwd-tries
  (renamed from passwd-tries for namespacing)

Etc-overrides (upstream-owned paths; staged by the PKGBUILD at
/usr/share/omarchy/etc-overrides/ and cp'd in by post_install):
- etc/security/faillock.conf (owned by pam)
- etc/nsswitch.conf (owned by filesystem)
- etc/cups/cups-browsed.conf (owned by cups-browsed)
- etc/plymouth/plymouthd.conf (owned by plymouth)

All sudoers files validate with visudo -cf.

The install scripts that previously wrote these files are updated or
removed in follow-up commits.

etc/nsswitch.conf

@@ -0,0 +1,19 @@
+# Name Service Switch configuration file.
+# See nsswitch.conf(5) for details.
+
+passwd: files systemd
+group: files [SUCCESS=merge] systemd
+shadow: files systemd
+gshadow: files systemd
+
+publickey: files
+
+hosts: mymachines mdns_minimal [NOTFOUND=return] resolve files myhostname dns
+networks: files
+
+protocols: files
+services: files
+ethers: files
+rpc: files
+
+netgroup: files