polish: fix page title, multi-select styling, chart colors

- Page title: "HiHala Data - Museums" -> "HiHala Data"
- Meta description: updated to "Event analytics"
- Multi-select dropdown: fix inherited uppercase, wider to fit labels
- Multi-select arrow: smooth CSS rotation instead of swapping characters
- Chart colors: 10-color palette for events/channels (was 3)
- Remove unused ArcElement (Doughnut) from Chart.js registration (-5KB)
- District chart uses dynamic palette instead of hardcoded 2 colors

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/App.css

@@ -796,16 +796,22 @@ table tbody tr:hover {
 }
 
 .multi-select-arrow {
-  font-size: 0.65rem;
-  opacity: 0.5;
+  font-size: 0.6rem;
+  opacity: 0.4;
   margin-inline-start: 8px;
+  transition: transform 150ms ease;
+}
+
+.multi-select-trigger[aria-expanded="true"] .multi-select-arrow {
+  transform: rotate(180deg);
 }
 
 .multi-select-dropdown {
   position: absolute;
   top: calc(100% + 4px);
   left: 0;
-  right: 0;
+  min-width: 100%;
+  width: max-content;
   background: var(--surface);
   border: 1px solid var(--border);
   border-radius: 8px;
@@ -816,6 +822,12 @@ table tbody tr:hover {
   padding: 4px;
 }
 
+.multi-select-dropdown,
+.multi-select-dropdown * {
+  text-transform: none;
+  letter-spacing: normal;
+}
+
 .multi-select-option {
   display: flex;
   align-items: center;
@@ -825,8 +837,6 @@ table tbody tr:hover {
   cursor: pointer;
   font-size: 0.875rem;
   color: var(--text-primary);
-  text-transform: none;
-  letter-spacing: normal;
   font-weight: normal;
 }