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>

client/src/pages/HomePage.css

@@ -0,0 +1,43 @@
+.home-page {
+  min-height: 100vh;
+  background: linear-gradient(180deg, #0f0f1a 0%, #1a1a2e 40%, #16213e 100%);
+}
+
+.site-header {
+  text-align: center;
+  padding: 24px 16px 8px;
+}
+
+.site-header h1 {
+  font-family: 'Georgia', 'Times New Roman', serif;
+  font-size: 32px;
+  color: #e8d5b5;
+  margin: 0;
+  letter-spacing: 2px;
+}
+
+.site-subtitle {
+  color: rgba(201, 169, 110, 0.6);
+  font-family: 'Georgia', serif;
+  font-size: 14px;
+  margin: 8px 0 0;
+  font-style: italic;
+}
+
+.loading {
+  text-align: center;
+  padding: 48px;
+  color: rgba(201, 169, 110, 0.6);
+  font-family: 'Georgia', serif;
+  font-size: 16px;
+}
+
+.error-banner {
+  margin: 16px;
+  padding: 12px 16px;
+  background: rgba(139, 0, 0, 0.3);
+  border: 1px solid rgba(255, 100, 100, 0.4);
+  border-radius: 6px;
+  color: #ffaaaa;
+  text-align: center;
+}