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/present.h

@@ -0,0 +1,24 @@
+#ifndef VGPU_PRESENT_H
+#define VGPU_PRESENT_H
+
+/* present.h — win32 present/pump lifecycle: staging arena, submit handoff, and
+ * the publish loop driving the OS-agnostic engine over ctx's region-view. */
+
+#include <stdint.h>
+#include "ctx.h"           /* win32 vgpu_ctx + vgpu_region_t */
+
+/* Initialize present/staging state inside ctx over an already-created region.
+ * Allocates the staging+cursor arena. Returns 0 on success. */
+int  vgpu_present_init(vgpu_ctx* ctx, vgpu_region_t* region, uint32_t default_fps);
+void vgpu_present_deinit(vgpu_ctx* ctx);
+
+/* Capture backends submit a freshly captured desktop frame (any source pitch).
+ * Repacked tight into ctx->content_buf, clamped to max mode. Thread-safe. */
+void vgpu_present_submit(vgpu_ctx* ctx, const uint8_t* bgra,
+                         uint32_t width, uint32_t height, uint32_t src_pitch);
+
+/* Run the publish pump: reconcile control, tick heartbeat, compose cursor,
+ * publish on change / on full_frame_req. Never returns (process lifetime). */
+void vgpu_present_run(vgpu_ctx* ctx);
+
+#endif /* VGPU_PRESENT_H */