feat(vinput): drop NPU/OpenVINO support (#384)

Vinput's streaming Zipformer models have unbounded dynamic shapes, so
OpenVINO cannot compile them for the GPU or the NPU; the `openvino`
provider and ai's Intel NPU enablement could never run on the NPU (noted
as unverified in WORKAROUNDS WA-017). Remove the backend option, the
daemon's OpenVINO library path, and the intel-npu module enable, and
update the eval test, README and WORKAROUNDS (drop WA-016 and WA-017).

Keep Vinput's stock package and its bundled sherpa-onnx (1.13.4): the
fork-based and nixpkgs-master sherpa overrides existed only to provide the
`openvino` provider, so drop package.nix with them.

Assisted-by: opencode (DeepSeek V4.1 Flash)

outputs/x86_64-linux/tests/idols-ai-voice-input/expected.nix

@@ -1,9 +1,5 @@
 {
   enablesLocalAsr = true;
   enablesLitePackage = false;
-  sherpaOnnxVersion = "1.13.8";
   hasVinputDaemon = true;
-  hasOpenvinoServer = false;
-  exposesNpuRuntimeLibraries = true;
-  enablesIntelNpu = true;
 }

outputs/x86_64-linux/tests/idols-ai-voice-input/expr.nix

@@ -6,21 +6,9 @@ let
   cfg = outputs.nixosConfigurations.ai-niri.config;
   hm = cfg.home-manager.users.ryan;
   packageNames = map (package: package.pname or "") hm.i18n.inputMethod.fcitx5.addons;
-  vinputPackage = builtins.head (
-    builtins.filter (
-      package: (package.pname or "") == "fcitx5-vinput"
-    ) hm.i18n.inputMethod.fcitx5.addons
-  );
-  daemonEnvironment = hm.systemd.user.services.vinput-daemon.Service.Environment;
 in
 {
   enablesLocalAsr = builtins.elem "fcitx5-vinput" packageNames;
   enablesLitePackage = builtins.elem "fcitx5-vinput-lite" packageNames;
-  sherpaOnnxVersion = vinputPackage.passthru.sherpaOnnxVersion or "";
   hasVinputDaemon = hm.systemd.user.services ? vinput-daemon;
-  hasOpenvinoServer = hm.systemd.user.services ? openvino-npu-stt;
-  exposesNpuRuntimeLibraries = builtins.any (
-    variable: builtins.match "LD_LIBRARY_PATH=.*:/run/opengl-driver/lib" variable != null
-  ) daemonEnvironment;
-  enablesIntelNpu = cfg.hardware.cpu.intel.npu.enable;
 }