Optimize installer: preflight checks, tuned conf, doctor, faster default

Layers a few things on top of the initial scaffold:

- Default to sunshine-bin (precompiled, ~seconds) instead of building from
  source. --from-source restores the old behavior.
- Add lib/preflight.sh: catches the gotchas before any work is done —
  Wayland session, NVIDIA driver responsive, nvidia-drm.modeset, amdgpu
  loaded, pipewire-pulse present, SSH-without-session warning.
- Add lib/config.sh: writes a tuned ~/.config/sunshine/sunshine.conf with
  per-vendor encoder settings (NVENC P1+ll+cbr, VAAPI ultralowlatency,
  QuickSync veryfast), KMS capture, pulse audio sink. Uses a
  "# managed-by: omarchy-moonlight" marker; removing it hands ownership
  back to the user and the installer won't touch the file again.
- Add lib/verify.sh: post-install verification of every step
  (cap_sys_admin set, group resolves, udev rule present, /dev/uinput
  exists, encoder reachable, service active, :47990 listening). Same
  checks are reachable standalone via --doctor.
- Install runtime helpers (pipewire-pulse, vulkan-tools, libva-utils)
  alongside Sunshine for diagnostics + audio.
- Uninstall handles both sunshine + sunshine-bin and the -bin moonlight
  variant.
- README documents the tuning table, the new flags, and the modeset
  troubleshooting path.

lib/packages.sh

@@ -1,17 +1,20 @@
 #!/usr/bin/env bash
 # Install Sunshine, Moonlight, and GPU-specific hardware-encode dependencies.
 
-# Default to source build (canonical AUR package). Override with SUNSHINE_PKG=sunshine-bin
-# in the environment for the precompiled build (much faster install).
-: "${SUNSHINE_PKG:=sunshine}"
+# Default to the precompiled AUR build for a fast install (~seconds instead of
+# the ~10 minute source compile). Override with SUNSHINE_PKG=sunshine to build
+# from source.
+: "${SUNSHINE_PKG:=sunshine-bin}"
+: "${MOONLIGHT_PKG:=moonlight-qt}"
 
 install_sunshine() {
+  # Ensure runtime deps useful for capture/diagnostics across vendors.
+  yay_install pipewire-pulse vulkan-tools libva-utils
   yay_install "$SUNSHINE_PKG"
 }
 
 install_moonlight() {
-  # moonlight-qt is in the AUR (also a -bin variant). yay handles both.
-  yay_install moonlight-qt
+  yay_install "$MOONLIGHT_PKG"
 }
 
 install_gpu_encoder_packages() {