plan: add freebsd-mDNSResponder + freebsd-DiskArbitration porting plans

Two more Apple-OSS userland tools for the launchd companion set.

freebsd-mdnsresponder-plan.html:
  Bonjour / zeroconf service discovery. .local hostnames, automatic
  printer / file-share discovery on the LAN. Apache 2.0; latest tag
  mDNSResponder-878.70.2; 261 source files, ~154k LOC. SURPRISE: zero
  Mach surface. Apple already maintains a cross-platform mDNSPosix
  platform layer (used by Linux/FreeBSD/Solaris builds). The port is
  much more a configuration exercise than a true port. Drop
  mDNSMacOSX/, mDNSWindows/, Apple-private extensions; use mDNSPosix
  as-is. Optional Phase 3 polish: swap PosixDaemon's select(2) loop
  for libdispatch sources to match the rest of our daemon stack.

freebsd-disk-arbitration-plan.html:
  Disk attach/detach events, mount/unmount/eject coordination,
  mount-policy approvals. APSL 2.0; latest tag DiskArbitration-79.3;
  71 source files, ~34.5k LOC; 10 Mach-tied. THE HARD ONE: Apple's
  daemon is IOKit-tied at its core (walks IOMedia objects in the I/O
  Registry). FreeBSD has no IOKit. Port replaces IOKit with libgeom
  for disk discovery + devctl(4) for hot-plug events. Real porting
  effort, not just IPC swap. Workspace File Viewer's "Devices" sidebar
  is the headline gershwin use case.

Both Phase 7+/8+ work. Index links them under the launchd entry.

Author: pkgdemon