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

app/services/data_service.py

@@ -84,6 +84,9 @@ class DataService:
                 await self.cache.set_json(cache_key, options_chain)
                 return options_chain
 
+            # Limit initial load to the nearest expirations so the page can render quickly.
+            expirations = expirations[:3]
+
             calls: list[dict[str, Any]] = []
             puts: list[dict[str, Any]] = []