Replace logbook backup v1 JSON with v2 ZIP archives.

ZIP .daagbok files use a compact manifest and binary KDAB blobs so large
photo, voice, and GPS payloads no longer inflate in a single JSON file.

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

client/package-lock.json

@@ -12,6 +12,7 @@
         "bip39": "^3.1.0",
         "dexie": "^4.4.2",
         "dexie-react-hooks": "^4.4.0",
+        "fflate": "^0.8.3",
         "i18next": "^26.3.0",
         "i18next-browser-languagedetector": "^8.2.1",
         "jspdf": "^4.2.1",