feat: add stock database with prisma for portfolio persistence

- Initialize Prisma with SQLite and Stock model
- Create database service layer with singleton client
- Add API routes for stock CRUD operations
- Integrate database with analyze page to persist ticker entries
- Add Playwright tests for stock database functionality

tests/stock-db.spec.ts

@@ -0,0 +1,31 @@
+import { test, expect } from "@playwright/test";
+
+test.describe("Stock Database", () => {
+  test("should add and list stocks", async ({ request }) => {
+    const uniqueTicker = `TEST${Date.now()}`;
+
+    const createRes = await request.post("/api/stocks", {
+      form: { ticker: uniqueTicker },
+    });
+    expect(createRes.ok()).toBeTruthy();
+
+    const listRes = await request.get("/api/stocks");
+    const stocks = await listRes.json();
+    expect(stocks).toContainEqual(expect.objectContaining({ ticker: uniqueTicker }));
+  });
+
+  test("should persist tickers after page reload", async ({ request, page }) => {
+    const uniqueTicker = `PERSIST${Date.now()}`;
+
+    await request.post("/api/stocks", {
+      form: { ticker: uniqueTicker },
+    });
+
+    await page.goto("/stocks");
+    await page.waitForLoadState("networkidle");
+
+    const listRes = await request.get("/api/stocks");
+    const stocks = await listRes.json();
+    expect(stocks).toContainEqual(expect.objectContaining({ ticker: uniqueTicker }));
+  });
+});