Add CSV/Excel calendar upload that maps posts into the monthly RRSS view.

Agency can import editorial calendars per tenant; pieces land on each day with the same month grid and day zoom as existing plans.

Co-authored-by: Cursor <cursoragent@cursor.com>

package.json

@@ -17,7 +17,8 @@
     "next": "15.1.7",
     "react": "^19.0.0",
     "react-dom": "^19.0.0",
-    "tailwind-merge": "^3.0.2"
+    "tailwind-merge": "^3.0.2",
+    "xlsx": "^0.18.5"
   },
   "devDependencies": {
     "@types/node": "^22.13.4",