feat: add reviewed postgres migration foundation

frontend/src/lib/db/client.ts

@@ -0,0 +1,18 @@
+import { drizzle, type NodePgDatabase } from "drizzle-orm/node-postgres";
+import { Pool } from "pg";
+
+export type DomainDatabase = { pool: Pool; db: NodePgDatabase };
+
+export function createDomainDatabase(
+  connectionString: string,
+  maxConnections = 5,
+): DomainDatabase {
+  const pool = new Pool({
+    connectionString,
+    max: maxConnections,
+    idleTimeoutMillis: 30_000,
+    connectionTimeoutMillis: 5_000,
+    application_name: "jyotisha-web",
+  });
+  return { pool, db: drizzle(pool) };
+}

frontend/src/lib/db/config.ts

@@ -0,0 +1,16 @@
+export type DatabaseUrlKey =
+  | "IDENTITY_DATABASE_URL"
+  | "APP_DATABASE_URL"
+  | "ADMIN_DATABASE_URL";
+
+export function readDatabaseUrl(
+  env: NodeJS.ProcessEnv,
+  key: DatabaseUrlKey,
+): string {
+  const value = env[key]?.trim();
+  if (!value) throw new Error(`${key} is required`);
+  if (!value.startsWith("postgresql://")) {
+    throw new Error(`${key} must be a PostgreSQL URL`);
+  }
+  return value;
+}