Enhance timeline and movement flow UI; add fetched painting images.

Timeline: era and historical-event click-to-zoom, event markers from historical-events.ts. Movement flow: shared zoom/pan, viewport-fit layout, curved lineage streams, hover-to-reveal artist lifespans on stacked lanes. Docs updated. Includes batch-fetched paintings and regenerated thumbs.
Co-authored-by: Cursor <cursoragent@cursor.com>

client/src/pages/HomePage.css

@@ -1,8 +1,18 @@
 .home-page {
-  min-height: 100vh;
+  height: 100vh;
+  overflow: hidden;
+  display: flex;
+  flex-direction: column;
   background: linear-gradient(180deg, #0f0f1a 0%, #1a1a2e 40%, #16213e 100%);
 }
 
+.home-movements-section {
+  flex: 1;
+  min-height: 0;
+  display: flex;
+  flex-direction: column;
+}
+
 .gallery-session-suspended {
   position: fixed;
   inset: 0;
@@ -21,6 +31,7 @@
 .site-header {
   text-align: center;
   padding: 24px 16px 8px;
+  flex-shrink: 0;
 }
 
 .site-header h1 {
@@ -47,6 +58,10 @@
   font-size: 16px;
 }
 
+.home-page > .timeline-wrapper {
+  flex-shrink: 0;
+}
+
 .error-banner {
   margin: 16px;
   padding: 12px 16px;