feat(worker): 直通渲染 stream copy 优化 - 无重编码性能提升10倍+

当输入片段与输出参数完全一致（h264/yuv420p/同分辨率/同帧率/无字幕/无特效）时，
走 FFmpeg stream copy 不重编码，性能提升 10 倍以上（典型场景 20s → 1-2s）。

核心改动：
1. probe_video_info 增强：返回编码/像素格式/音频信息（用于 copy 条件判断）
2. _can_use_stream_copy：7项条件检查（编码/分辨率/帧率/像素格式/字幕/trim等）
3. _try_render_stream_copy：stream copy 执行，失败自动回退到重编码
4. 单clip直通场景先尝试 stream copy，不满足或失败再回退带滤镜的直通渲染
5. trim 用 -ss/-t 实现，无需滤镜，copy 模式下也能用

安全保障：
- 条件不满足自动跳过，不影响现有渲染质量
- FFmpeg 失败自动回退到重编码，不影响成功率
- 输出文件为空时判定失败并清理损坏文件

测试：9个新增单测 + 现有75个统一渲染测试，全绿 ✅
（含条件判断、成功路径、失败回退、完整渲染流程等场景）

apps/worker/video_processing/ffmpeg_utils.py

@@ -163,10 +163,14 @@ def probe_duration(local_path: str | Path) -> float:
 
 
 def probe_video_info(video_path: str) -> dict[str, Any]:
-    """获取视频信息（宽、高、时长、fps）。
+    """获取视频信息（宽、高、时长、fps、编码、像素格式）。
 
     Returns:
-        {"width": int, "height": int, "duration": float, "fps": float}
+        {
+            "width": int, "height": int, "duration": float, "fps": float,
+            "video_codec": str, "audio_codec": str, "pix_fmt": str,
+            "has_audio": bool,
+        }
         失败时返回默认值。
     """
     try:
@@ -175,10 +179,8 @@ def probe_video_info(video_path: str) -> dict[str, Any]:
                 FFPROBE_BIN,
                 "-v",
                 "error",
-                "-select_streams",
-                "v:0",
                 "-show_entries",
-                "stream=width,height,r_frame_rate,duration",
+                "stream=width,height,r_frame_rate,duration,codec_name,codec_type,pix_fmt",
                 "-show_entries",
                 "format=duration",
                 "-of",
@@ -195,14 +197,19 @@ def probe_video_info(video_path: str) -> dict[str, Any]:
         import json
 
         info = json.loads(result.stdout)
-        stream = info.get("streams", [{}])[0]
+        streams = info.get("streams", [])
         fmt = info.get("format", {})
 
-        width = int(stream.get("width", DEFAULT_OUTPUT_WIDTH))
-        height = int(stream.get("height", DEFAULT_OUTPUT_HEIGHT))
+        video_stream = next((s for s in streams if s.get("codec_type") == "video"), {})
+        audio_stream = next((s for s in streams if s.get("codec_type") == "audio"), {})
+
+        width = int(video_stream.get("width", DEFAULT_OUTPUT_WIDTH))
+        height = int(video_stream.get("height", DEFAULT_OUTPUT_HEIGHT))
+        video_codec = video_stream.get("codec_name", "") or ""
+        pix_fmt = video_stream.get("pix_fmt", "") or ""
 
         # 解析帧率
-        fps_str = stream.get("r_frame_rate", "25/1")
+        fps_str = video_stream.get("r_frame_rate", "25/1")
         if "/" in fps_str:
             num, den = fps_str.split("/")
             fps = float(num) / float(den) if float(den) > 0 else DEFAULT_FPS
@@ -210,13 +217,20 @@ def probe_video_info(video_path: str) -> dict[str, Any]:
             fps = float(fps_str) if fps_str else DEFAULT_FPS
 
         # 时长
-        duration = float(fmt.get("duration", 0)) or float(stream.get("duration", 0))
+        duration = float(fmt.get("duration", 0)) or float(video_stream.get("duration", 0))
+
+        has_audio = bool(audio_stream)
+        audio_codec = audio_stream.get("codec_name", "") or ""
 
         return {
             "width": width,
             "height": height,
             "duration": duration,
             "fps": round(fps, 2),
+            "video_codec": video_codec,
+            "audio_codec": audio_codec,
+            "pix_fmt": pix_fmt,
+            "has_audio": has_audio,
         }
     except Exception as e:
         logger.warning("获取视频信息失败: %s, error: %s", video_path, e)
@@ -225,6 +239,10 @@ def probe_video_info(video_path: str) -> dict[str, Any]:
             "height": DEFAULT_OUTPUT_HEIGHT,
             "duration": 0.0,
             "fps": DEFAULT_FPS,
+            "video_codec": "",
+            "audio_codec": "",
+            "pix_fmt": "",
+            "has_audio": True,
         }