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/src/sources/user-sources.ts

@@ -0,0 +1,79 @@
+import { and, eq } from "drizzle-orm"
+
+import type { Database } from "../db/index.ts"
+
+import { userSources } from "../db/schema.ts"
+import { SourceNotFoundError } from "./errors.ts"
+
+export function sources(db: Database, userId: string) {
+	return {
+		/** Returns all enabled sources for the user. */
+		async enabled() {
+			return db
+				.select()
+				.from(userSources)
+				.where(and(eq(userSources.userId, userId), eq(userSources.enabled, true)))
+		},
+
+		/** Returns a specific source by ID, or undefined. */
+		async find(sourceId: string) {
+			const rows = await db
+				.select()
+				.from(userSources)
+				.where(and(eq(userSources.userId, userId), eq(userSources.sourceId, sourceId)))
+				.limit(1)
+
+			return rows[0]
+		},
+
+		/** Enables a source for the user. Throws if the source row doesn't exist. */
+		async enableSource(sourceId: string) {
+			const rows = await db
+				.update(userSources)
+				.set({ enabled: true, updatedAt: new Date() })
+				.where(and(eq(userSources.userId, userId), eq(userSources.sourceId, sourceId)))
+				.returning({ id: userSources.id })
+
+			if (rows.length === 0) {
+				throw new SourceNotFoundError(sourceId, userId)
+			}
+		},
+
+		/** Disables a source for the user. Throws if the source row doesn't exist. */
+		async disableSource(sourceId: string) {
+			const rows = await db
+				.update(userSources)
+				.set({ enabled: false, updatedAt: new Date() })
+				.where(and(eq(userSources.userId, userId), eq(userSources.sourceId, sourceId)))
+				.returning({ id: userSources.id })
+
+			if (rows.length === 0) {
+				throw new SourceNotFoundError(sourceId, userId)
+			}
+		},
+
+		/** Creates or updates the config for a source. */
+		async upsertConfig(sourceId: string, config: Record<string, unknown>) {
+			await db
+				.insert(userSources)
+				.values({ userId, sourceId, config })
+				.onConflictDoUpdate({
+					target: [userSources.userId, userSources.sourceId],
+					set: { config, updatedAt: new Date() },
+				})
+		},
+
+		/** Updates the encrypted credentials for a source. Throws if the source row doesn't exist. */
+		async updateCredentials(sourceId: string, credentials: Buffer) {
+			const rows = await db
+				.update(userSources)
+				.set({ credentials, updatedAt: new Date() })
+				.where(and(eq(userSources.userId, userId), eq(userSources.sourceId, sourceId)))
+				.returning({ id: userSources.id })
+
+			if (rows.length === 0) {
+				throw new SourceNotFoundError(sourceId, userId)
+			}
+		},
+	}
+}