feat: migrate schema to DATE type, add test infrastructure

- Migrate due_date/next_occurrence columns from TIMESTAMPTZ to DATE
- Update serializeRow() to distinguish DATE vs TIMESTAMPTZ serialization
- Simplify frontend date parsing (no more timezone workarounds)
- Add Vitest + Testing Library test infrastructure
- Add initial date parsing/formatting unit tests
- Update package.json with dev dependencies (vitest, testing-library, jsdom)

start.sh

@@ -0,0 +1,17 @@
+#!/bin/sh
+set -e
+echo "Waiting for PostgreSQL at $DB_HOST:$DB_PORT..."
+for i in $(seq 1 60); do
+  if nc -z "$DB_HOST" "$DB_PORT" 2>/dev/null; then
+    echo "PostgreSQL is ready"
+    break
+  fi
+  echo "Waiting... $i"
+  sleep 1
+done
+
+echo "Running migrations..."
+tsx ./migrate.ts
+
+echo "Starting VixTix..."
+exec node server.js