feat(content): swap cosmos Orion to a text-free SVS flythrough

Replaces the JPL "Orion: Dust and Death" primary (captioned throughout — we'd
cropped it, losing framing) with STScI's "Flight Through the Orion Nebula"
(visible light, NASA SVS 30957) — a full-frame, text-free flythrough of the same
nebula. Sourced via the content pipeline (trim 10–34s + crossfade-loop → 1080p
master + base); cosmos-orbit / abyss-cosmos transitions regenerated from it.

- build_pool_manifest META: cosmos -> SVS 30957, license CC-BY-class (NASA/ESA/
  STScI), new trim window.
- Remove the now-obsolete decaption_cosmos() crop helper (the new source needs
  no caption removal).
- docs/content-candidate-pool.md: record the source swap; drop the crop note.

269 passed, 2 skipped. New clip verified text-free + full-frame by-eye;
final look to be confirmed by the operator.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

simulator/build_pool_manifest.py

@@ -55,8 +55,9 @@ CCBY_STSCI = "CC-BY-class — credit NASA, ESA, STScI"
 # --- Per-clip provenance: id -> (title, license, source) ---
 META: dict[str, tuple[str, str, str]] = {
     # cosmos
-    "cosmos": ("Orion Nebula flythrough (NASA/JPL-Caltech)", PD,
-               "NASA/JPL-Caltech — images.nasa.gov JPL-20221122-SOLSYSf-0001 (Orion); trim ~30–54s, crossfade-loop"),
+    "cosmos": ("Orion Nebula flythrough (NASA/ESA/STScI)", CCBY_STSCI,
+               "NASA SVS 30957 orion_vis-1920x1080 (Flight Through the Orion Nebula, visible light); "
+               "trim 10–34s, crossfade-loop. Text-free — replaces the captioned JPL 'Dust and Death' clip."),
     "cosmos_galaxies": ("Flying Through Galaxies (NASA SVS)", PD,
                         "NASA SVS a014950 14950_Galaxies_FlyThrough_4k; trim 8–32s, crossfade-loop"),
     "cosmos_hudf": ("Hubble Ultra Deep Field zoom (NASA/ESA/STScI)", CCBY_STSCI,
@@ -408,35 +409,6 @@ def generate_media() -> None:
         print(f"generated transitions/{a}-{b}.mp4 (+ .rev) from real bases")
 
 
-# Fraction of frame HEIGHT kept (from the top) to drop the NASA burned-in
-# lower-third captions on the cosmos Orion clip ("DUST FILAMENT", "BLUE BUBBLE",
-# …). The "Orion: Dust and Death" visualization is captioned throughout, so
-# trimming can't avoid them — we crop past them instead. ~1.5x tighter framing.
-COSMOS_CAPTION_KEEP = 0.66
-
-
-def decaption_cosmos() -> None:
-    """Re-crop the cosmos Orion base/master IN PLACE to remove NASA's burned-in
-    lower-third caption band, keeping 16:9 (crop width to match, center-x, top-
-    anchored) then re-fitting to 1920x1080. Run ONCE after (re)sourcing the Orion
-    clip — re-running would crop again. Media is gitignored, so this is the
-    recorded, reproducible form of the operation."""
-    ff = _ffmpeg()
-    f = COSMOS_CAPTION_KEEP
-    vf = f"crop=iw*{f}:ih*{f}:iw*{(1 - f) / 2}:0,scale=1920:1080"
-    for name, crf in (("base", "20"), ("master", "18")):
-        p = MEDIA / "cosmos" / f"{name}.mp4"
-        if not p.exists():
-            continue
-        tmp = p.with_suffix(".decap.mp4")
-        subprocess.run([
-            ff, "-y", "-i", str(p), "-vf", vf,
-            "-c:v", "libx264", "-crf", crf, "-pix_fmt", "yuv420p", "-an", str(tmp),
-        ], check=True, capture_output=True)
-        tmp.replace(p)
-        print(f"de-captioned cosmos/{name}.mp4 (kept top {int(f * 100)}%)")
-
-
 def main(argv: list[str]) -> None:
     manifest = build_manifest()
     MANIFEST.write_text(json.dumps(manifest, indent=2, ensure_ascii=False) + "\n")