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>

package.json

@@ -8,6 +8,7 @@
     "@testing-library/react": "^16.3.2",
     "@testing-library/user-event": "^13.5.0",
     "chart.js": "^4.5.1",
+    "chartjs-plugin-annotation": "^3.1.0",
     "chartjs-plugin-datalabels": "^2.2.0",
     "html2canvas": "^1.4.1",
     "jszip": "^3.10.1",