feat: season filter + chart bands on Dashboard and Comparison

Dashboard:
- Season dropdown filter (filters data by season date range)
- Revenue trend chart shows colored annotation bands for each season
- All downstream memos use season-filtered data

Comparison:
- Season presets in period selector (optgroup)
- Auto-compares with same season from previous hijri year if defined
- Season preset persists start/end dates in URL

Added chartjs-plugin-annotation for chart bands.

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

src/config/chartConfig.ts

@@ -12,6 +12,7 @@ import {
   Filler
 } from 'chart.js';
 import ChartDataLabels from 'chartjs-plugin-datalabels';
+import Annotation from 'chartjs-plugin-annotation';
 
 // Register ChartJS components once
 ChartJS.register(
@@ -25,7 +26,8 @@ ChartJS.register(
   Tooltip,
   Legend,
   Filler,
-  ChartDataLabels
+  ChartDataLabels,
+  Annotation
 );
 
 export const chartColors = {