Rework Byzantine hall as a late-antique basilica interior.

Replace the flat gold-mosaic chapel with marble revetment walls, a
Cosmatesque stone floor, and a coffered timber ceiling, matching
Santa Sabina / San Vitale reference interiors.

New procedural surfaces in galleryProceduralTextures.ts:
- marble-revetment: book-matched veined panels in moulded travertine
  surrounds (each panel mirrored about its centre)
- marble-opus-sectile: cut-stone bays with diagonal diamond inlays and
  corner triangles in porphyry, verd-antique, giallo, and grey
- coffered-wood: recessed walnut coffers with lit beam chamfers

Add a byzantine detail set to MovementHallDetails.tsx: engaged porphyry
colonnettes with white-marble basket capitals and impost blocks carrying
the ceiling, a marble revetment dado, and hanging brass polycandela.
Colonnettes stay flush in the corner pockets so they do not clip the
~0.7m frame hang margin.

Basilicas are lit by shafts from high windows rather than evenly
flooded, but the shared hall lights carry a brightness floor that
prevented dimming. Add an opt-in lightScale to the interior style that
scales the scene, hall, track, and HDR environment lights. It defaults
to 1, so all other halls are unchanged; only Byzantine opts down. Window
fill lights are left unscaled so the daylight shafts still read.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Documentation/basics.md

@@ -335,12 +335,12 @@ Enter from the home page by clicking a **movement name** on the movement flow. F
 | Paintings on walls | **Left, end, and right** — single-wing halls keep the far wall solid (full span); multi-wing halls hang end-wall works on panels beside the back exit |
 | Wall order | Same U-shaped hang as artist halls (left → end → right) |
 | Frame captions | **Year · artist** label below each frame |
-| Period interior | Each of the 26 seeded movements maps to a unique style in `movement-interior-styles.ts` (Italian palazzo, Baroque palace, NYC loft, white cube, etc.). Style keys use a legacy id map (`DB_ID_TO_STYLE_KEY`: gallery ids **1–26** → authored keys **27–52**, with Northern/High Renaissance swapped) so Byzantine gets the chapel, not Gothic stone |
-| Wall materials | Hi-res **procedural textures** with normal maps (`galleryProceduralTextures.ts`): real-world stone, marble, wood panelling, brick, velvet, stucco — plus **single-colour painted walls** (`painted-lime`, `painted-oil-matte`, `painted-oil-satin`, `painted-emulsion`, `painted-flat`) tinted per movement for Renaissance salons through modern white cubes |
+| Period interior | Each of the 26 seeded movements maps to a unique style in `movement-interior-styles.ts` (Italian palazzo, Baroque palace, Byzantine basilica, NYC loft, white cube, etc.). Style keys use a legacy id map (`DB_ID_TO_STYLE_KEY`: gallery ids **1–26** → authored keys **27–52**, with Northern/High Renaissance swapped) so Byzantine gets the basilica, not Gothic stone |
+| Wall materials | Hi-res **procedural textures** with normal maps (`galleryProceduralTextures.ts`): real-world stone, marble, wood panelling, brick, velvet, stucco, **marble revetment** (framed book-matched panels), **Cosmatesque paving** (`marble-opus-sectile`), **coffered timber** ceilings — plus **single-colour painted walls** (`painted-lime`, `painted-oil-matte`, `painted-oil-satin`, `painted-emulsion`, `painted-flat`) tinted per movement for Renaissance salons through modern white cubes |
 | Textures | Wall/floor/ceiling maps applied via `useTexturedMaterial`; movement **tints** drive painted-wall hue |
 | Windows | **Side walls only** — placed in gaps between frames when possible; if a wall is packed, high **clerestory** windows are still added so the hall keeps daylight (`computeSideWallWindows`) |
 | Lighting | Shared hall lights only (ambient / hemisphere / directional + capped ceiling track spots + one fill per window). See **light budget** below |
-| Period details | `MovementHallDetails.tsx` — classical / neoclassical use **shallow engaged corner pilasters** (never freestanding mid-hall or proud corner shafts that cover frames) |
+| Period details | `MovementHallDetails.tsx` — classical / neoclassical use **shallow engaged corner pilasters** (never freestanding mid-hall or proud corner shafts that cover frames); `byzantine` adds engaged porphyry colonnettes with basket capitals, a marble revetment dado, and hanging brass polycandela |
 | Back wall | Single wing: solid display wall. Multi-wing: **Exit double doors** → **Wing navigator** or **Exit to Timeline** |
 | Front / entrance wall | Single wing: **Exit double doors** (leave the way you entered). Multi-wing: **“Next wing →”** archway when a later wing exists |
 | Influence lamps | Same golden upside-down emissive fixtures as artist halls when `has_influence_links` is true |
@@ -376,6 +376,8 @@ Full guide: [tours.md](tours.md).
 
 **Light budget (critical):** Three.js forward shading cannot compile `MeshStandardMaterial` with dozens of dynamic lights. Large wings used to add **one `spotLight` per painting** (plus influence lamps), which pushed the scene to ~100–200 lights — walls, floor, and ceiling then rendered as a black void while painting canvases (`MeshBasicMaterial`) still showed. Halls therefore use **shared lighting only**: ambient / hemisphere / directional fill, a small set of ceiling track spots (`GalleryTrackLights`, capped), and **one** window spot each. Painting canvases stay unlit (`MeshBasicMaterial`); frames and influence fixtures use **emissive** accents instead of per-frame lights. Intensities are scaled for three.js physical lights (post-r155).
 
+Shared lights carry a **brightness floor** so dark period styles never render as a black void. A style that is *meant* to be dim (a basilica lit by window shafts, not flooded) sets **`lightScale`** in `movement-interior-styles.ts` — it multiplies the scene ambient/hemisphere/directional/fill lights, the hall point lights, the ceiling track spots, and the HDR `environmentIntensity`. It defaults to **1**, so only styles that opt in are affected. Window fill lights are deliberately **not** scaled, so the daylight shafts still read against the darker room.
+
 **Period architecture:** Freestanding columns must not sit in the walkway or in the corner pocket in front of frames (hang margin is only ~0.7 m from each wall end). Classical / neoclassical details use **engaged corner pilasters** flush to the walls (`MovementHallDetails.tsx`).
 
 **Surface textures:** Procedural colour maps use sRGB; **normal maps use `NoColorSpace`** (`galleryProceduralTextures.ts`). Wrong colour space on normals breaks wall shading.