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/components/Dashboard.tsx

@@ -3,7 +3,7 @@ import { useSearchParams } from 'react-router-dom';
 import { Line, Bar } from 'react-chartjs-2';
 import { Carousel, EmptyState, FilterControls, MultiSelect, StatCard } from './shared';
 import { ExportableChart } from './ChartExport';
-import { chartColors, createBaseOptions } from '../config/chartConfig';
+import { chartColors, chartPalette, createBaseOptions } from '../config/chartConfig';
 import { useLanguage } from '../contexts/LanguageContext';
 import {
   filterData,
@@ -206,15 +206,16 @@ function Dashboard({ data, showDataLabels, setShowDataLabels, includeVAT, setInc
         labels: museums,
         datasets: [{
           data: museums.map(m => grouped[m].visitors),
-          backgroundColor: [chartColors.primary + 'cc', chartColors.secondary + 'cc', chartColors.tertiary + 'cc'],
-          borderWidth: 0
+          backgroundColor: museums.map((_, i) => chartPalette[i % chartPalette.length] + 'cc'),
+          borderWidth: 0,
+          borderRadius: 4
         }]
       },
       revenue: {
         labels: museums,
         datasets: [{
           data: museums.map(m => grouped[m].revenue),
-          backgroundColor: [chartColors.primary + 'cc', chartColors.secondary + 'cc', chartColors.tertiary + 'cc'],
+          backgroundColor: museums.map((_, i) => chartPalette[i % chartPalette.length] + 'cc'),
           borderRadius: 4
         }]
       }
@@ -229,7 +230,7 @@ function Dashboard({ data, showDataLabels, setShowDataLabels, includeVAT, setInc
       labels: channels,
       datasets: [{
         data: channels.map(d => grouped[d].revenue),
-        backgroundColor: [chartColors.secondary + 'cc', chartColors.tertiary + 'cc'],
+        backgroundColor: channels.map((_, i) => chartPalette[i % chartPalette.length] + 'cc'),
         borderRadius: 4
       }]
     };
@@ -243,7 +244,7 @@ function Dashboard({ data, showDataLabels, setShowDataLabels, includeVAT, setInc
       labels: districtNames,
       datasets: [{
         data: districtNames.map(d => grouped[d].revenue),
-        backgroundColor: [chartColors.primary + 'cc', chartColors.secondary + 'cc', chartColors.tertiary + 'cc', chartColors.muted + 'cc'],
+        backgroundColor: districtNames.map((_, i) => chartPalette[i % chartPalette.length] + 'cc'),
         borderRadius: 4
       }]
     };