feat(ux): Sprint 3 mobile nav, sync conflicts, and resilience

Improve mobile bottom navigation, accessible dialogs and cards, explicit
sync conflict resolution, i18n error messages, encrypted draft autosave,
and persistent storage hints for offline data safety.

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

client/src/i18n/locales/en.json

@@ -13,6 +13,17 @@
       "sv": "Svenska",
       "nb": "Norsk"
     },
+    "dialog": {
+      "ok": "OK",
+      "yes": "Yes",
+      "no": "No"
+    },
+    "errors": {
+      "load_failed": "Could not load data.",
+      "save_failed": "Could not save changes.",
+      "delete_failed": "Could not delete.",
+      "export_failed": "Export failed."
+    },
     "common": {
       "unsaved_changes_title": "Unsaved changes",
       "unsaved_changes_message": "You have unsaved changes. Leave this page anyway? Your changes will be lost.",
@@ -92,13 +103,18 @@
       "update_title": "Update available",
       "update_desc": "A new version of Kapteins Daagbok is ready. Reload to get the latest changes.",
       "update_now": "Reload now",
-      "update_reloading": "Reloading…"
+      "update_reloading": "Reloading…",
+      "storage_persist_hint": "Your browser may delete offline data. Allow persistent storage to keep your logbook safe (browser settings or when prompted)."
     },
     "sync": {
       "status_synced": "Synced",
       "status_syncing": "Syncing…",
       "status_offline": "Offline Cache",
-      "status_unsynced": "Unsynced changes"
+      "status_unsynced": "Unsynced changes",
+      "conflict_title": "Sync conflict",
+      "conflict_message": "{{count}} change(s) could not be synced (entry {{id}}…). Choose which version to keep.",
+      "conflict_use_server": "Use server version",
+      "conflict_keep_local": "Keep my version"
     },
     "vessel": {
       "title": "Vessel Master Data",