feat(neptune): add a Voyager 2 map assembled from the 1989 approach frames

[alowpoly]

Neptune's Hubble map is soft because Hubble sees the planet only about 58 pixels wide. Neptune now has a Voyager 2 dataset: one color map assembled here from 89 NASA frames of August 1989, about three times finer on screen. Hubble 2025 stays the default. Uranus is unchanged; its ledger records why no sharper map exists. Bodies: Neptune, Uranus (ledger only). Details: Neptune README.

• Placement: each frame is fitted to the limb of the flattened planet. Residual: median 0.45 px, largest 0.98 px.
• Clouds: frames are carried to one moment by drift measured between frame pairs (2.67 to 2.83° per hour westward round the Great Dark Spot) and the published Voyager wind fit elsewhere.
• Color: from the 17–18 August sets, registered band by band; the mean color is tied to the Irwin et al. 2024 reconstruction.
• Size: the manifest gains 178 entries, one per frame file. The 89 labels (356 KB) are tracked; the frames restore from PDS.

Limits: Chrome only. North of 34.8° N is gray grid. Clouds in unmatched bands take their band's mean color. 51 frames borrow the twist of the nearest recorded attitude.

• Baked neptune once, published to R2, inventory committed.

Clean: map tests 12 of 12; observed-surfaces, runtime-contract, scene-contract and source-record tests; authoring typecheck; ESLint; hash, ledger, body-reference and ownership checks; check-assets-published.

PR rules: titles, PDS4 provenance and ISO plain language.