Add headless streaming mode + Mac client + full docs

Headless mode (new) — for KVM-attached hosts streaming to disconnected clients
- --headless / --mirror flags; default headless on hostname JARVIS, mirror elsewhere
- New lib/headless.sh installs prep-cmd hooks to ~/.local/share/omarchy-moonlight/bin
- bin/sunshine-stream-do.sh creates/resizes a Hyprland HEADLESS-1 output to the
  connecting client's resolution and migrates the active workspace onto it
- bin/sunshine-stream-undo.sh tears down the headless output on disconnect and
  returns the workspace to a non-headless monitor when one is available
- lib/config.sh writes capture=wlr, output_name=HEADLESS-1, and the JSON
  global_prep_cmd entry referencing the installed hook paths
- lib/preflight.sh adds a preflight_headless step that checks hyprctl, jq, and
  a running Hyprland session (warn-only, install can proceed)
- lib/verify.sh adds checks for the hook scripts and the wlr/global_prep_cmd
  config lines

Mac client
- client/install-macos.sh: Darwin guard, Homebrew presence check, brew cask
  install of Moonlight, idempotent
- client/README.md: per-platform install (macOS / Android / iOS / Apple TV /
  Linux + Steam Deck) and the five-step first-pair walkthrough

Other
- jq added to the helper install set in lib/packages.sh (hooks parse Hyprland
  JSON output)
- README.md rewritten to cover both modes, the new flags, the tuned defaults
  per mode + per vendor, the headless internals, and the client pointer

lib/packages.sh

@@ -9,7 +9,7 @@
 
 install_sunshine() {
   # Ensure runtime deps useful for capture/diagnostics across vendors.
-  yay_install pipewire-pulse vulkan-tools libva-utils
+  yay_install pipewire-pulse vulkan-tools libva-utils jq
   yay_install "$SUNSHINE_PKG"
 }