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/preflight.sh

@@ -8,6 +8,7 @@ preflight_all() {
   preflight_gpu
   preflight_kms_modeset
   preflight_audio
+  preflight_headless
 }
 
 preflight_session() {
@@ -96,3 +97,33 @@ preflight_audio() {
     warn "pipewire-pulse is not installed. Audio capture may not work until it is."
   fi
 }
+
+preflight_headless() {
+  # Only relevant in headless mode. Checks are non-fatal: install can proceed
+  # even if Hyprland isn't reachable right now (hooks just won't function until
+  # the user logs into Hyprland on the host).
+  [[ "${STREAM_MODE:-}" == "headless" ]] || return 0
+
+  if command -v hyprctl >/dev/null 2>&1; then
+    ok "hyprctl on PATH"
+  else
+    warn "hyprctl not found. Headless prep-cmd hooks will fail until Hyprland is installed and reachable."
+  fi
+
+  if pkg_installed jq; then
+    ok "jq installed (prep-cmd hooks have their parser)"
+  else
+    info "jq not installed yet — will be installed in the packages step."
+  fi
+
+  if [[ -n "${HYPRLAND_INSTANCE_SIGNATURE:-}" ]]; then
+    ok "Hyprland instance signature present in environment"
+  else
+    local rt="${XDG_RUNTIME_DIR:-/run/user/$(id -u)}"
+    if compgen -G "$rt/hypr/*/" >/dev/null 2>&1; then
+      ok "Hyprland runtime directory found under $rt/hypr/"
+    else
+      warn "Hyprland does not appear to be running. Install will proceed; hooks will only work once you log into Hyprland on the host."
+    fi
+  fi
+}