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_high_profile_bitrate.py

@@ -0,0 +1,67 @@
+"""Tests for the High-quality profile fill-the-disc bitrate math."""
+
+from devedeng.project import compute_high_profile_bitrate as calc
+
+CAP_KB = 3_780_000.0  # 4.2 GB * 0.90 margin, in kBytes
+FLOOR = 3000
+CAP = 9000
+
+
+def audio_kbits(rate_kbps, runtime_s, streams=1):
+    return rate_kbps * streams * runtime_s
+
+
+def test_short_movie_one_disc_at_cap():
+    # 30 min: tiny, so bitrate is pinned at the 9000k cap, one disc
+    n, br = calc(1800, audio_kbits(448, 1800), CAP_KB)
+    assert n == 1
+    assert br == CAP
+
+
+def test_two_hours_fills_one_disc():
+    n, br = calc(7200, audio_kbits(448, 7200), CAP_KB)
+    assert n == 1
+    assert FLOOR <= br <= CAP
+    # should be comfortably above the floor (filling the disc)
+    assert br > 3500
+
+
+def test_four_hours_two_discs():
+    n, br = calc(14400, audio_kbits(448, 14400), CAP_KB)
+    assert n == 2
+    assert FLOOR <= br <= CAP
+
+
+def test_eight_hours_multiple_discs():
+    n, br = calc(28800, audio_kbits(448, 28800), CAP_KB)
+    assert n >= 3
+    assert br >= FLOOR
+
+
+def test_zero_runtime_guard():
+    assert calc(0, 0, CAP_KB) == (1, CAP)
+
+
+def test_bitrate_always_within_bounds():
+    for rt in (300, 1800, 3600, 7200, 14400, 30000, 60000):
+        n, br = calc(rt, audio_kbits(448, rt), CAP_KB)
+        assert FLOOR <= br <= CAP, (rt, br)
+        assert n >= 1
+
+
+def test_filled_content_does_not_exceed_disc_capacity():
+    # the chosen bitrate must not overflow the n discs it claims to fill
+    for rt in (1800, 7200, 14400, 28800):
+        ak = audio_kbits(448, rt)
+        n, br = calc(rt, ak, CAP_KB)
+        used_kbits = br * rt + ak
+        assert used_kbits <= n * CAP_KB * 8 + 1  # +1 for rounding slack
+
+
+def test_menu_reservation_reduces_video_budget():
+    rt = 7200
+    ak = audio_kbits(448, rt)
+    n0, br0 = calc(rt, ak, CAP_KB, menu_kbytes=0)
+    n1, br1 = calc(rt, ak, CAP_KB, menu_kbytes=200_000)
+    # with a menu eating space, the fill bitrate can only be <= the no-menu one
+    assert br1 <= br0