Inventory split: InventoryItem entity, schema v2 with tested migration, Lager screen

Stock, package size and prescription state move to inventory_item;
medication is now a regimen (itemId FK RESTRICT — deleting a stock item
can never silently take adherence history with it). Supply warnings
aggregate consumption across all regimens sharing an item. New Lager
screen with one-tap '+1 pakning' restock; med editor picks an existing
item or creates one inline via the shared ItemFormState (one form, no
drift). Backup format v2 mirrors the split and still restores v1 files
by performing the same conversion the DB migration does.

MIGRATION_1_2 statements are copied from the exported 2.json and proven
by an instrumented MigrationTestHelper test on the emulator (validates
against the schema AND asserts data survival) before it ever touches
the phone's medical record. Heads-up: connectedAndroidTest must target
the emulator (ANDROID_SERIAL) — the phone's release signature rejects
debug test APKs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/src/main/java/no/naiv/meddetsamme/backup/BackupManager.kt

@@ -18,7 +18,12 @@ class BackupManager(private val context: Context) {
     /** Plaintext JSON export (caller decides whether/how to encrypt). */
     suspend fun exportJson(): String {
         val dao = db.backupDao()
-        return BackupSerializer.export(dao.allMedications(), dao.allDoseTimes(), dao.allDoseLogs())
+        return BackupSerializer.export(
+            dao.allInventoryItems(),
+            dao.allMedications(),
+            dao.allDoseTimes(),
+            dao.allDoseLogs(),
+        )
     }
 
     /** Export encrypted with a *typed* passphrase (never stored — manual path). */