perf(video): 新增 RKMPP DMA 采集编码通路并完善恢复逻辑

支持原生 HDMI 和 UVC 缓冲区导出，增加同步 RKMPP 编码及可选 MJPEG 硬件转码。
校验帧布局和缓冲区租约，在 DMA 不可用或编码失败时回退到复制通路。
保留自定义码率和 GOP 策略，重开采集时同步 HDMI 源帧率，并区分 UVC 超时状态。

验证：88 个视频测试通过（含 4 个新增回归测试）；ARM64 cargo check --tests 通过。

libs/hwcodec/cpp/ffmpeg_hw/rkmpp_dma_jpeg.h

@@ -0,0 +1,38 @@
+#pragma once
+#include <stddef.h>
+#include <stdint.h>
+
+// Validate bounded JPEG headers before giving hardware a fixed-size output
+// buffer. Only baseline 8-bit JPEG is accepted; other streams use copy fallback.
+// No scan-data traversal or full-packet copy is needed.
+inline bool rkmpp_dma_jpeg_header(const uint8_t *data, size_t size, int width, int height) {
+    if (!data || size < 4 || data[0] != 0xff || data[1] != 0xd8) return false;
+    size_t pos = 2;
+    bool sof = false;
+    while (pos < size) {
+        if (data[pos++] != 0xff) return false;
+        while (pos < size && data[pos] == 0xff) ++pos;
+        if (pos == size) return false;
+        const unsigned marker = data[pos++];
+        if (!marker || marker == 0xd8 || marker == 0xd9 || marker == 1 ||
+            (marker >= 0xd0 && marker <= 0xd7)) return false;
+        if (size - pos < 2) return false;
+        const size_t length = (size_t(data[pos]) << 8) | data[pos + 1];
+        if (length < 2 || length > size - pos) return false;
+        if (marker == 0xc0) {
+            if (sof || length < 8 || data[pos + 2] != 8) return false;
+            const unsigned h = (unsigned(data[pos + 3]) << 8) | data[pos + 4];
+            const unsigned w = (unsigned(data[pos + 5]) << 8) | data[pos + 6];
+            const unsigned components = data[pos + 7];
+            if (w != unsigned(width) || h != unsigned(height) ||
+                (components != 1 && components != 3) || length != 8 + 3 * components) return false;
+            sof = true;
+        } else if (marker >= 0xc0 && marker <= 0xcf && marker != 0xc4 && marker != 0xcc) {
+            return false; // Progressive, lossless, extended or differential SOF.
+        } else if (marker == 0xda) {
+            return sof && length >= 6 && size - pos > length;
+        }
+        pos += length;
+    }
+    return false;
+}