vgpu in-guest producer in-tree, release CI, flexible vmie discovery

- src/si/vgpu-stream: in-guest vgpu producer built as a Windows cross-compiled target (if(WIN32))
- .gitea: release workflow — cross-build the agent and build/publish the deb against system vmie
- cmake/makefile: resolve vmie from a source tree (LIBVMIE_PATH) or installed libvmie-dev

src/si/vgpu-stream/win32/capture-win32.h

@@ -0,0 +1,19 @@
+#ifndef VGPU_CAPTURE_WIN32_H
+#define VGPU_CAPTURE_WIN32_H
+
+/* capture-win32.h — private win32 plumbing shared by the capture backends.
+ * Not part of the OS-agnostic capture seam (see src/stream/include/capture.h):
+ * it depends on the win32 vgpu_ctx and the thread-handoff convention. */
+
+#include "ctx.h"            /* win32 vgpu_ctx (full definition) */
+
+/* Thread argument passed to capture threads via LPVOID. Heap-allocated by the
+ * backend's *_start, owned and freed by the thread. Carries the explicit ctx
+ * (no global state) plus per-backend state pointer. */
+typedef struct {
+    vgpu_ctx* ctx;
+    int       fps;
+    void*     backend_state;   /* opaque per-backend handle block */
+} capture_thread_arg;
+
+#endif /* VGPU_CAPTURE_WIN32_H */