Fix pay_date NaN: parse DATE columns as strings in pg

pg returns DATE columns as JS Date objects which serialize to ISO
timestamps, causing split('-') to produce NaN for the day portion.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

server/src/db.js

@@ -1,6 +1,9 @@
-const { Pool } = require('pg');
+const { Pool, types } = require('pg');
 const { runMigrations } = require('../../db/migrations/001_initial_schema');
 
+// Return DATE columns as plain YYYY-MM-DD strings instead of JS Date objects
+types.setTypeParser(1082, val => val);
+
 const pool = new Pool({
   connectionString: process.env.DATABASE_URL,
 });