feat(backend): add DB persistence layer (#79)

* feat(backend): add DB persistence layer

Replace raw pg Pool with Drizzle ORM backed by Bun.sql.
Add per-user source configuration table (user_sources).
Migrate Better Auth to drizzle-adapter.
Add AES-256-GCM credential encryption.

Co-authored-by: Ona <no-reply@ona.com>

* fix(backend): set updatedAt explicitly in all mutations

onConflictDoUpdate bypasses Drizzle's $onUpdate hook.
Set updatedAt explicitly in all mutation methods.

Co-authored-by: Ona <no-reply@ona.com>

* fix(backend): add composite index on user_sources

Add (user_id, enabled) index for the enabled() query path.

Co-authored-by: Ona <no-reply@ona.com>

---------

Co-authored-by: Ona <no-reply@ona.com>

apps/aelis-backend/drizzle.config.ts

@@ -0,0 +1,10 @@
+import { defineConfig } from "drizzle-kit"
+
+export default defineConfig({
+	out: "./drizzle",
+	schema: "./src/db/schema.ts",
+	dialect: "postgresql",
+	dbCredentials: {
+		url: process.env.DATABASE_URL!,
+	},
+})