Backup: versioned JSON serializer, SigV4 + S3 client, JCE crypto, daily worker

Milestone 5. One BackupManager entry point so export, import and
auto-backup share the same serializer and crypto by construction.
Explicit DTOs decouple the backup contract from the Room schema.
JCE baseline (PBKDF2-HMAC-SHA256 600k → AES-256-GCM) behind the
BackupCrypto interface with format auto-detection on decrypt; age
lands behind the same interface in milestone 6. SigV4 signer verified
against AWS's published documentation example signature. Settings in
SharedPreferences encrypted under a non-exportable AndroidKeyStore key
— replaces the now fully deprecated androidx security-crypto with the
same construction (~70 lines, zero deps); threat-model comments state
plainly that the stored auto-backup passphrase only protects against
bucket compromise. WorkManager daily periodic job, inexact by design.

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

app/src/main/java/no/naiv/meddetsamme/data/BackupDao.kt

@@ -0,0 +1,51 @@
+package no.naiv.meddetsamme.data
+
+import androidx.room.Dao
+import androidx.room.Insert
+import androidx.room.Query
+import androidx.room.Transaction
+
+/**
+ * Bulk read/replace for backup. Inserts preserve original ids (autoGenerate
+ * only kicks in for id = 0), which keeps FK references in the file intact.
+ */
+@Dao
+interface BackupDao {
+
+    @Query("SELECT * FROM medication")
+    suspend fun allMedications(): List<Medication>
+
+    @Query("SELECT * FROM dose_time")
+    suspend fun allDoseTimes(): List<DoseTime>
+
+    @Query("SELECT * FROM dose_log")
+    suspend fun allDoseLogs(): List<DoseLog>
+
+    @Query("DELETE FROM medication")
+    suspend fun clearMedications()
+
+    @Insert
+    suspend fun insertMedications(meds: List<Medication>)
+
+    @Insert
+    suspend fun insertDoseTimes(doseTimes: List<DoseTime>)
+
+    @Insert
+    suspend fun insertDoseLogs(logs: List<DoseLog>)
+
+    /**
+     * Replace-all restore. Deleting medication CASCADEs to dose_time and
+     * dose_log, so one delete clears everything; insertion order respects FKs.
+     */
+    @Transaction
+    suspend fun replaceAll(
+        meds: List<Medication>,
+        doseTimes: List<DoseTime>,
+        logs: List<DoseLog>,
+    ) {
+        clearMedications()
+        insertMedications(meds)
+        insertDoseTimes(doseTimes)
+        insertDoseLogs(logs)
+    }
+}