build: package universal Windows runtime and verify automatic CPU fallback

docs/evidence/windows-package-cpu-fallback.json

@@ -0,0 +1,12 @@
+{
+  "architecture": "x86_64",
+  "verified_files": 13,
+  "archive_sha256": "7fa9ccc87ee4fdd0d539898853c47e5b125b42518337a4a2d8393e98c54fb8b8",
+  "worker_requested_device": "auto",
+  "worker_actual_device": "cpu",
+  "no_gpu_condition": "GGML_DISABLE_VULKAN=1 only in child; SEARCHI_FORCE_CPU absent",
+  "worker_startup_query_and_exit_ms": 2509.7244000062346,
+  "query_dimensions": 768,
+  "decoder": "ffprobe version n9.0.2-27-g7e93014c5b-20261012 Copyright (c) 2007-2026 the FFmpeg developers",
+  "scope": "Real packaged worker default-mode CPU fallback with disabled provider; no GPU, native UI or clean-machine certification"
+}