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

AGENTS.md

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+# AGENTS.md
+
+## Engineering Rules
+
+1. **Always close the test loop.**
+   - Do not stop after code changes.
+   - Run the app locally.
+   - Run real tests against the running app.
+   - For UI work, prefer real browser tests (Playwright) over assumptions.
+   - Verify the exact route/page that changed.
+
+2. **Local Docker first, deploy later.**
+   - Use local Docker/OrbStack for fast feedback.
+   - Only deploy after local behavior is verified.
+
+3. **Browser-visible behavior beats log-only confidence.**
+   - A route returning HTML is not sufficient.
+   - Confirm page content renders and no runtime/500 error is visible.
+
+4. **When using parallel worktrees, preserve shared domain models.**
+   - New feature branches must not silently remove compatibility types used elsewhere.
+   - In this project, `LombardPortfolio` is still required by strategy/core modules.
+
+5. **Do not claim a feature is live unless the UI is wired to it.**
+   - Backend service existence is not enough.
+   - The rendered page must actually consume the live data path.
+
+## Project Learnings
+
+### NiceGUI layout constraint
+- `ui.header()` must be a top-level page layout element.
+- Do not nest `ui.header()` inside `ui.column()` or other containers.
+
+### Options page performance lesson
+- Loading all expiries/chains before first paint can make the page appear broken.
+- Prefer rendering fast, then loading data incrementally.
+
+### FastAPI/NiceGUI integration lesson
+- NiceGUI page handlers should not assume `request.app.state.*` is always the right access path for shared services.
+- Use an explicit runtime/service registry if needed.
+
+### Docker development lesson
+- Avoid mounting the whole repo over `/app` when the image contains required runtime scripts.
+- Mount narrower paths in dev (`./app`, `./config`) to preserve image-managed files like entrypoints.
+
+## Validation Checklist for UI Changes
+- [ ] Local Docker stack starts cleanly
+- [ ] `/health` returns OK
+- [ ] Changed page opens in browser automation
+- [ ] No visible 500/runtime error
+- [ ] Screenshot artifact captured
+- [ ] Relevant logs checked