Add digital catalog with shareable flipbook and ktg.montzar.ir deploy files.

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

.env.example

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+PORT=3000
+API_PORT=3010
+PUBLIC_BASE_URL=http://localhost:3000
+STORAGE_DIR=./storage
+DATABASE_PATH=./data/catalogs.sqlite
+
+# Production (server /var/www/ktg) — see deploy/DEPLOY.md
+# NODE_ENV=production
+# PORT=3020
+# PUBLIC_BASE_URL=https://ktg.montzar.ir
+# STORAGE_DIR=/var/www/ktg/storage
+# DATABASE_PATH=/var/www/ktg/data/catalogs.sqlite