test: add Playwright browser tests and document test loop

- add real browser test for overview and options pages
- document engineering learnings in AGENTS.md
- commit NiceGUI header layout fix
- limit options initial expirations for faster first render

tests/test_e2e_playwright.py

@@ -0,0 +1,31 @@
+from __future__ import annotations
+
+from pathlib import Path
+
+from playwright.sync_api import Page, expect, sync_playwright
+
+BASE_URL = "http://127.0.0.1:8000"
+ARTIFACTS = Path("tests/artifacts")
+ARTIFACTS.mkdir(parents=True, exist_ok=True)
+
+
+def test_homepage_and_options_page_render() -> None:
+    with sync_playwright() as p:
+        browser = p.chromium.launch(headless=True)
+        page = browser.new_page(viewport={"width": 1440, "height": 1000})
+
+        page.goto(BASE_URL, wait_until="networkidle", timeout=30000)
+        expect(page).to_have_title("NiceGUI")
+        expect(page.locator("text=Vault Dashboard").first).to_be_visible(timeout=10000)
+        expect(page.locator("text=Overview").first).to_be_visible(timeout=10000)
+        page.screenshot(path=str(ARTIFACTS / "overview.png"), full_page=True)
+
+        page.goto(f"{BASE_URL}/options", wait_until="domcontentloaded", timeout=30000)
+        expect(page.locator("text=Options Chain").first).to_be_visible(timeout=15000)
+        expect(page.locator("text=Filters").first).to_be_visible(timeout=15000)
+        body_text = page.locator("body").inner_text(timeout=15000)
+        assert "Server error" not in body_text
+        assert "RuntimeError" not in body_text
+        page.screenshot(path=str(ARTIFACTS / "options.png"), full_page=True)
+
+        browser.close()