Add BooksSyncContext, refine database schema, and enhance synchronization support

- Introduce `BooksSyncContext` for managing book synchronization states (server-only, local-only, to-sync, etc.).
- Remove `UserContext` and related dependencies.
- Refine localization strings (`en.json`) with sync-related updates (e.g., "toSyncFromServer", "toSyncToServer").
- Extend database schema with additional tables and fields for syncing books, chapters, and related entities.
- Add `last_update` fields and update corresponding repository methods to support synchronization logic.
- Enhance IPC handlers with stricter typing, data validation, and sync-aware operations.

lib/locales/en.json

@@ -115,7 +115,13 @@
   "bookCard": {
     "noCoverAlt": "No cover",
     "initialsSeparator": ".",
-    "subtitlePlaceholder": "No subtitle"
+    "subtitlePlaceholder": "No subtitle",
+    "synced": "Synced",
+    "localOnly": "Local only",
+    "serverOnly": "Server only",
+    "toSyncFromServer": "Download from server",
+    "toSyncToServer": "Upload to server",
+    "sync": "Sync"
   },
   "scribeTopBar": {
     "logoAlt": "Logo",

lib/locales/fr.json

@@ -115,7 +115,13 @@
   "bookCard": {
     "noCoverAlt": "Pas de couverture",
     "initialsSeparator": ".",
-    "subtitlePlaceholder": "Aucun sous-titre"
+    "subtitlePlaceholder": "Aucun sous-titre",
+    "synced": "Synchronisé",
+    "localOnly": "Local uniquement",
+    "serverOnly": "Sur le serveur uniquement",
+    "toSyncFromServer": "Télécharger depuis le serveur",
+    "toSyncToServer": "Envoyer vers le serveur",
+    "sync": "Synchroniser"
   },
   "scribeTopBar": {
     "logoAlt": "Logo",