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-lock.json

@@ -13,6 +13,7 @@
         "@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",
@@ -1571,6 +1572,15 @@
         "pnpm": ">=8"
       }
     },
+    "node_modules/chartjs-plugin-annotation": {
+      "version": "3.1.0",
+      "resolved": "https://registry.npmjs.org/chartjs-plugin-annotation/-/chartjs-plugin-annotation-3.1.0.tgz",
+      "integrity": "sha512-EkAed6/ycXD/7n0ShrlT1T2Hm3acnbFhgkIEJLa0X+M6S16x0zwj1Fv4suv/2bwayCT3jGPdAtI9uLcAMToaQQ==",
+      "license": "MIT",
+      "peerDependencies": {
+        "chart.js": ">=4.0.0"
+      }
+    },
     "node_modules/chartjs-plugin-datalabels": {
       "version": "2.2.0",
       "resolved": "https://registry.npmjs.org/chartjs-plugin-datalabels/-/chartjs-plugin-datalabels-2.2.0.tgz",