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/main.c

@@ -0,0 +1,55 @@
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+#include "region.h"        /* win32 pinned region */
+#include "ctx.h"           /* win32 vgpu_ctx (embeds region-view) */
+#include "present.h"       /* present/pump lifecycle */
+#include "stream.h"        /* OS-agnostic status/error/backend setters */
+#include "capture.h"       /* backend table */
+
+int main(int argc, char** argv) {
+    int fps = argc > 1 ? atoi(argv[1]) : 30;
+    if (fps <= 0) fps = 30;
+
+    vgpu_region_t region;
+    if (vgpu_region_create(&region) != 0) {
+        fprintf(stderr, "main: region_create failed\n");
+        return 1;
+    }
+
+    vgpu_ctx ctx;
+    if (vgpu_present_init(&ctx, &region, (uint32_t)fps) != 0) {
+        fprintf(stderr, "main: present_init failed\n");
+        vgpu_region_destroy(&region);
+        return 1;
+    }
+
+    const char* eyes = getenv("EYES");
+    int n = 0;
+    const capture_backend* bks = capture_backends(&n);
+    int started = 0;
+    for (int i = 0; i < n && !started; i++) {
+        if (eyes && _stricmp(eyes, bks[i].name) != 0) continue;
+        fprintf(stderr, "eyes: trying %s\n", bks[i].name);
+        started = bks[i].start(&ctx, fps);
+        if (!started) fprintf(stderr, "eyes: %s unavailable\n", bks[i].name);
+    }
+    if (!started) {
+        fprintf(stderr, "eyes: no capture backend available\n");
+        vgpu_set_status(&ctx.view, VGPU_ST_ERROR);
+        vgpu_set_error(&ctx.view, 2u);
+        vgpu_present_deinit(&ctx);
+        vgpu_region_destroy(&region);
+        return 1;
+    }
+
+    vgpu_set_backend(&ctx.view, ctx.backend);
+    vgpu_present_run(&ctx);   /* never returns */
+
+    vgpu_present_deinit(&ctx);
+    vgpu_region_destroy(&region);
+    return 0;
+}