Redesign 3D gallery as single hall per artist with exit navigation.

Restore React client source, add hall-to-hall navigation via painting influences grouped by movement, and update documentation.

Co-authored-by: Cursor <cursoragent@cursor.com>

Documentation/API.md

@@ -92,6 +92,41 @@ Full artist profile for the bio page and 3D gallery entry.
 
 ---
 
+## `GET /api/artists/:id/navigation`
+
+Related artists for hall-to-hall navigation at the exit doorway. Derived from `painting_influences`:
+
+- **Predecessors** — artists whose works influenced this artist’s paintings.
+- **Successors** — artists whose works were influenced by this artist’s paintings.
+
+Both lists are grouped by art movement and exclude the current artist.
+
+**Response**
+
+```json
+{
+  "predecessors": [
+    {
+      "movement_id": 4,
+      "movement_name": "Early Renaissance",
+      "movement_color": "#B8860B",
+      "artists": [
+        {
+          "id": 12,
+          "name": "Domenico Ghirlandaio",
+          "birth_year": 1448,
+          "death_year": 1494,
+          "portrait_path": "portraits/Domenico_Ghirlandaio.jpg"
+        }
+      ]
+    }
+  ],
+  "successors": []
+}
+```
+
+---
+
 ## `POST /api/artists/:id/preload-images`
 
 Fast local scan: links paintings to files already on disk. Does **not** download from the internet (safe to call before opening the 3D gallery).
@@ -146,6 +181,7 @@ The React client wraps these endpoints in `client/src/api/client.ts`:
 | `api.getTimeline(start, end)` | `GET /api/timeline` |
 | `api.getArtists(...)` | `GET /api/artists` |
 | `api.getArtist(id)` | `GET /api/artists/:id` |
+| `api.getArtistNavigation(id)` | `GET /api/artists/:id/navigation` |
 | `api.getPainting(id)` | `GET /api/paintings/:id` |
 | `preloadArtistImages(id)` | `POST /api/artists/:id/preload-images` |
 | `imageUrl(path)` | `/images/<path>` or placeholder |