feat: migrate from SQLite to PostgreSQL - complete schema and API updates

- Remove better-sqlite3, add pg driver
- Convert schema to PostgreSQL types (serial, timestamp, boolean, jsonb)
- Generate fresh PostgreSQL migrations
- Update database connection layer with pg.Pool
- Fix all API routes: remove JSON.parse/stringify, use native timestamps and booleans
- Update drizzle.config.ts and .env.example for PostgreSQL

src/app/api/upload/route.ts

@@ -85,7 +85,6 @@ export async function POST(request: NextRequest): Promise<NextResponse> {
             // Create the chart
             const [newChart] = await db.insert(charts).values({
               name: chartName,
-              created_at: Math.floor(Date.now() / 1000),
             }).returning();
 
             // Parse and prepare candle data
@@ -99,9 +98,10 @@ export async function POST(request: NextRequest): Promise<NextResponse> {
                 if (isNaN(date.getTime())) {
                   throw new Error(`Invalid date format: ${row.time}`);
                 }
-                timestamp = Math.floor(date.getTime() / 1000);
+                timestamp = date; // PostgreSQL timestamp type expects Date object or ISO string
               } else if (typeof row.time === 'number') {
-                timestamp = row.time;
+                // If Unix timestamp (seconds), convert to Date
+                timestamp = new Date(row.time * 1000);
               } else {
                 throw new Error(`Invalid time value: ${row.time}`);
               }