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/auth.ts

@@ -0,0 +1,18 @@
+// Used by Better Auth CLI for schema generation.
+// Run: bunx --bun auth@latest generate --config auth.ts --output src/db/auth-schema.ts
+import { betterAuth } from "better-auth"
+import { drizzleAdapter } from "better-auth/adapters/drizzle"
+import { SQL } from "bun"
+import { drizzle } from "drizzle-orm/bun-sql"
+
+const client = new SQL({ url: process.env.DATABASE_URL })
+const db = drizzle({ client })
+
+export const auth = betterAuth({
+	database: drizzleAdapter(db, { provider: "pg" }),
+	emailAndPassword: {
+		enabled: true,
+	},
+})
+
+export default auth