Add pytest suite and CI (roadmap A1)

37 headless tests covering the logic that is cheap to break:
- split planner: plan_disc_split, chapter helpers (whole-fit, multi-disc
  partition, single-movie chapter/even-cut split, contiguous coverage)
- High-profile fill-disc bitrate math (disc count + bounds + capacity)
- ffmpeg command generation: profiles, text/image hardsub, 2-pass, nice,
  progress-to-file, even pad/crop + positive offsets, -ss seek, and the
  AC3 448k audio-clamp regression
- ffprobe subtitle detection: text/image classification, tags/disposition

tests/conftest.py makes the in-tree package importable and installs the
gettext _ builtin so modules run headless. Forgejo Actions workflow runs
the suite on push/PR. Update CLAUDE.md's testing section accordingly.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_ffprobe_detection.py

@@ -0,0 +1,82 @@
+"""Tests for embedded subtitle detection in ffprobe.process_json."""
+
+import json
+import devedeng.ffprobe
+
+
+def _probe(streams):
+    p = devedeng.ffprobe.ffprobe()
+    data = json.dumps({"streams": streams})
+    err = p.process_json("/movies/input.mkv", data)
+    return p, err
+
+
+def _video(index=0, duration="120.0"):
+    return {"index": index, "codec_type": "video", "codec_name": "h264",
+            "width": 1920, "height": 1080, "avg_frame_rate": "24/1",
+            "duration": duration}
+
+
+def _audio(index=1):
+    return {"index": index, "codec_type": "audio", "codec_name": "aac",
+            "sample_rate": "48000"}
+
+
+def _sub(index, codec, language="eng", title="", default=0, forced=0):
+    return {"index": index, "codec_type": "subtitle", "codec_name": codec,
+            "tags": {"language": language, "title": title},
+            "disposition": {"default": default, "forced": forced}}
+
+
+def test_no_subtitles_empty_list():
+    p, err = _probe([_video(), _audio()])
+    assert err is False
+    assert p.subtitle_tracks == []
+
+
+def test_text_subtitle_classified_text():
+    p, _ = _probe([_video(), _audio(), _sub(2, "subrip", "eng", default=1)])
+    assert len(p.subtitle_tracks) == 1
+    t = p.subtitle_tracks[0]
+    assert t["index"] == 2
+    assert t["codec"] == "subrip"
+    assert t["language"] == "eng"
+    assert t["kind"] == "text"
+    assert t["default"] is True
+    assert t["forced"] is False
+
+
+def test_image_subtitles_classified_image():
+    for codec in ("hdmv_pgs_subtitle", "dvd_subtitle", "dvdsub", "pgssub", "xsub"):
+        p, _ = _probe([_video(), _audio(), _sub(2, codec)])
+        assert p.subtitle_tracks[0]["kind"] == "image", codec
+
+
+def test_various_text_codecs_classified_text():
+    for codec in ("subrip", "ass", "ssa", "mov_text", "webvtt"):
+        p, _ = _probe([_video(), _audio(), _sub(2, codec)])
+        assert p.subtitle_tracks[0]["kind"] == "text", codec
+
+
+def test_multiple_subtitle_tracks_in_order():
+    p, _ = _probe([
+        _video(), _audio(),
+        _sub(2, "subrip", "eng", default=1),
+        _sub(3, "hdmv_pgs_subtitle", "fre", forced=1),
+        _sub(4, "ass", "jpn", title="Signs"),
+    ])
+    assert [t["index"] for t in p.subtitle_tracks] == [2, 3, 4]
+    assert [t["kind"] for t in p.subtitle_tracks] == ["text", "image", "text"]
+    assert p.subtitle_tracks[1]["forced"] is True
+    assert p.subtitle_tracks[2]["title"] == "Signs"
+
+
+def test_missing_tags_and_disposition_defaults():
+    # a subtitle stream with no tags/disposition must not crash
+    p, _ = _probe([_video(), _audio(),
+                   {"index": 2, "codec_type": "subtitle",
+                    "codec_name": "subrip"}])
+    t = p.subtitle_tracks[0]
+    assert t["language"] == ""
+    assert t["default"] is False
+    assert t["forced"] is False