feat(pipeline): resolve bundled ffmpeg fallback; integration test runs on real forest base

- run.py: add resolve_ffmpeg() mirroring setup_scales_media.py; change
  process_clip ff param to None and resolve at call time
- test_pipeline_integration.py: gate on resolve_ffmpeg() not PATH ffmpeg;
  verify proxy dims with cv2 instead of ffprobe
- ffmpeg_ops.py: add fps= to trim segments in crossfade_loop_args so xfade
  receives CFR input (xfade rejects 1/0 rate from raw trim output)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/test_pipeline_integration.py

@@ -1,25 +1,34 @@
-import shutil
-import subprocess
 from pathlib import Path
 
 import pytest
 
-from tools.pipeline.run import process_clip
+from tools.pipeline.run import process_clip, resolve_ffmpeg
 
-_HAS_FF = shutil.which("ffmpeg") is not None and shutil.which("ffprobe") is not None
 _FOREST = Path("simulator/sample_media/forest/base.mp4")
 
 
-@pytest.mark.skipif(not _HAS_FF, reason="ffmpeg/ffprobe not installed")
+def _ffmpeg_available() -> bool:
+    try:
+        resolve_ffmpeg()
+        return True
+    except Exception:
+        return False
+
+
+_HAS_FF = _ffmpeg_available()
+
+
+@pytest.mark.skipif(not _HAS_FF,
+                    reason="neither system ffmpeg nor imageio-ffmpeg available")
 @pytest.mark.skipif(not _FOREST.exists(),
                     reason="forest POC base absent (run simulator/setup_sample_media.py)")
 def test_process_clip_emits_proxy_and_master(tmp_path):
     out = process_clip(_FOREST, tmp_path, overlap=0.5, start=0.0, duration=4.0)
     assert out["proxy"].exists() and out["master"].exists()
-    # Proxy is exactly 1920x1080.
-    probe = subprocess.run(
-        ["ffprobe", "-v", "quiet", "-select_streams", "v:0",
-         "-show_entries", "stream=width,height", "-of", "csv=p=0", str(out["proxy"])],
-        capture_output=True, text=True, check=True,
-    ).stdout.strip()
-    assert probe == "1920,1080"
+    # Proxy is exactly 1920×1080 — verified with cv2, no ffprobe dependency.
+    import cv2
+    cap = cv2.VideoCapture(str(out["proxy"]))
+    w = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
+    h = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))
+    cap.release()
+    assert (w, h) == (1920, 1080)