fix(sunshine): use Intel rendering and recover remote Niri sessions (#268)

- render Niri on the Intel iGPU while retaining NVIDIA-connected physical outputs
- encode Sunshine streams with Intel VAAPI and wait for a Niri output before startup
- load VKMS persistently for headless sessions and configure `Virtual-1` at 2560x1600@60
- let Moonlight request the stream bitrate instead of enforcing a 20 Mbps host cap
- remove unsupported Dynamic Boost and global NVIDIA session overrides
- grant Sunshine access to virtual input devices
- add a Nushell recovery helper that starts a temporary greetd/Niri session from SSH
- identify and safely replace normal, standalone, or previous transient Niri sessions
- launch the transient service in the background and verify greetd, Niri, and Sunshine before returning
- ignore local `.worktrees` directories and keep eval regression coverage focused on structural behavior

modules/nixos/desktop/networking/sunshine/README.md

@@ -0,0 +1,34 @@
+# Temporary remote session recovery
+
+When a remote-only machine is stuck at the `greetd` TUI, run the Nushell helper from an
+SSH session to start one complete PAM/logind Wayland session without changing
+the persistent NixOS configuration:
+
+```bash
+sudo nu ./remote-session.nu
+```
+
+The helper validates its dependencies before changing the current session. It
+then stops the normal `greetd` service, starts a transient systemd-managed
+`greetd` configuration on `/dev/tty1`, and runs Niri directly. It returns after
+greetd, Niri, and Sunshine are ready. Tailscale is not affected.
+
+The `Virtual-1` output is created persistently by the `vkms` configuration in
+`hosts/idols-ai/hardware-intel.nix` and configured by
+`hosts/idols-ai/niri-hardware.kdl`. It gives Niri and Sunshine a capture target
+when both physical monitors attached to the NVIDIA GPU are off. The output also
+exists during normal physical sessions; keeping an idle virtual framebuffer has
+minor GPU and memory overhead.
+
+Options:
+
+```text
+-u USER       session user (defaults to SUDO_USER)
+-t TTY        tty device, for example /dev/tty2
+-c COMMAND    Wayland session command (defaults to niri --session)
+-f, --force   replace an existing Niri session without confirmation
+--check       validate prerequisites without changing service state
+```
+
+A reboot or a manual restart of `greetd.service` restores the normal TUI
+configuration.