feat(content): swap cosmos primary to the Webb "Cosmic Cliffs" flythrough

Operator found the Orion SVS 30957 flythrough merely good and asked for a more
dramatic nebula. Replaces the cosmos-scale primary with STScI's "Exploring the
Cosmic Cliffs in 3D" (Carina Nebula, Webb NIRCam — NASA SVS 31348), sourced from
its 4K master (Clifs-3d-STScI.mp4, 3840x2160) via the content pipeline:
trim 10-34s (clears the title card ~8s and end-credit card ~102s) + crossfade-loop
-> 4K master + supersampled 1080p base (5.5 Mbps, crisper than the old 2.9 Mbps
1080p-native Orion encode).

- build_pool_manifest META: cosmos -> SVS 31348 Cosmic Cliffs, new CCBY_WEBB
  credit (NASA, ESA, CSA, STScI). Labels retuned for the Carina framing
  (emission nebula / protostar; redshift -> distance ~7,500 ly).
- Regenerated manifest.json (also corrects stale JPL-Orion provenance left when
  129bb23 updated META but not the manifest) + all ring-edge transitions from the
  new base (cosmos-orbit / abyss-cosmos now zoom from the Cosmic Cliffs).
- docs/content-candidate-pool.md: record the swap + history.

269 passed, 2 skipped. New base verified text-free + full-frame by-eye across the
loop; final look to be confirmed by the operator (no Chrome on the box).

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

docs/content-candidate-pool.md

@@ -27,15 +27,18 @@ stays non‑commercial**.
 
 | id | clip | source | window (s) | license / credit |
 |----|------|--------|-----------|------------------|
-| `cosmos` | Orion Nebula flythrough | NASA SVS 30957 — https://svs.gsfc.nasa.gov/30957/ (`orion_vis-1920x1080.mp4`, *Flight Through the Orion Nebula*, visible light) | 10–34 | CC‑BY‑class — credit **NASA, ESA, STScI** |
+| `cosmos` | Cosmic Cliffs — Carina Nebula flythrough | NASA SVS 31348 — https://svs.gsfc.nasa.gov/31348/ (`Clifs-3d-STScI.mp4`, *Exploring the Cosmic Cliffs in 3D*, Webb NIRCam, **4K**) | 10–34 | CC‑BY‑class — credit **NASA, ESA, CSA, STScI** |
 
-> ℹ️ **Orion source swapped to a text-free clip (2026-06-25).** The original
-> primary was NASA/JPL's *"Orion: Dust and Death"* — an annotated visualization
-> with lower-third captions ("DUST FILAMENT", "BLUE BUBBLE", …) burned in
-> throughout, so trimming couldn't avoid them and a crop lost framing. Replaced
-> with STScI's **Flight Through the Orion Nebula** (visible light, SVS 30957) —
-> a full-frame, text-free flythrough of the same nebula. The earlier crop helper
-> (`decaption_cosmos`) is gone; no caption removal is needed for this source.
+> ℹ️ **Cosmos primary swapped to the Webb "Cosmic Cliffs" flythrough (2026-06-25, session 0018).**
+> History: the original primary was NASA/JPL's *"Orion: Dust and Death"* (captions
+> burned in → cropping lost framing); it was then swapped to STScI's text-free
+> *Flight Through the Orion Nebula* (SVS 30957, visible light). The operator found
+> the Orion clip merely good and asked for a more dramatic nebula, so the primary is
+> now STScI's **Exploring the Cosmic Cliffs in 3D** (Carina Nebula, Webb NIRCam,
+> **SVS 31348**) — a full-frame, text-free 3D flythrough sourced from its **4K**
+> master (`Clifs-3d-STScI.mp4`, 3840×2160) → supersampled 1080p base + 4K master.
+> Trim 10–34s clears the opening title card (gone by ~8s) and the end-credit card
+> (~102s). The earlier `decaption_cosmos` crop helper remains removed.
 | `cosmos_galaxies` | Flying Through Galaxies | NASA SVS — https://svs.gsfc.nasa.gov/vis/a010000/a014900/a014950/14950_Galaxies_FlyThrough_4k.mp4 | 8–32 | PD |
 | `cosmos_hudf` | Hubble Ultra Deep Field zoom | NASA SVS — https://svs.gsfc.nasa.gov/vis/a030000/a030600/a030687/hudf-b-1920x1080p30.mov | 20–44 | CC‑BY‑class — credit **NASA, ESA, STScI** |
 | `cosmos_xdf` | eXtreme Deep Field flythrough | NASA SVS — https://svs.gsfc.nasa.gov/vis/a030000/a030600/a030681/hxdf_fly-b-1920x1080p30.mov | 2–26 | CC‑BY‑class — credit **NASA, ESA, STScI** |
@@ -43,8 +46,8 @@ stays non‑commercial**.
 > ⚠️ **DISCREPANCY to fix next session.** Operator selected cosmos **#1, #3
 > (Orion), #4, #5**. During processing, **#6 Galaxy Traverse was run by mistake
 > instead of #3 Orion**. The cosmos primary now lives at
-> `simulator/sample_media/cosmos/base.mp4` as the text-free SVS 30957 flythrough
-> (see the Orion note above). **`cosmos_traverse` is an UNSELECTED extra on disk — drop it** (or
+> `simulator/sample_media/cosmos/base.mp4` as the Webb Cosmic Cliffs flythrough
+> (SVS 31348 — see the cosmos-primary note above). **`cosmos_traverse` is an UNSELECTED extra on disk — drop it** (or
 > confirm with operator). The current ring scale id is `cosmos`; when the pool is
 > wired, `cosmos` becomes one pool member.
 
@@ -116,5 +119,5 @@ Removed from local media (all were gitignored, so repo-invisible):
 - `forest` — the old Yosemite base, superseded by the `coast` pool. **dropped.**
 - `reef` — the original placeholder/early reef base, superseded by `reef_*`. **dropped.**
 - `orbit` / `abyss` — the Increment‑1 single real bases (NASA ISS Exp65 / ctenophore),
-  not in the new pools. **dropped** (the cosmos Orion base stays as the cosmos pool primary).
+  not in the new pools. **dropped** (the cosmos base — now the Webb Cosmic Cliffs flythrough, SVS 31348 — stays as the cosmos pool primary).
 - `review.html` gallery — now `.gitignore`d (local‑only, re‑buildable).