fix(windows): wrap pinnedCards Zustand selector in useShallow

[Aryansharma28]

Symptom

App starts but the window is blank. DevTools shows:

```
Warning: The result of getSnapshot should be cached to avoid an infinite loop
at BoardView (BoardView.tsx:43:119)
→ Error: Maximum update depth exceeded.
```

React unmounts the entire tree → nothing renders.

Cause

```ts
// BoardView.tsx:24 — before
const pinnedCards = useBoardStore((s) => s.pinnedCards());
```

`pinnedCards()` is a computed helper that returns a freshly `.filter().sort()`-ed array on every call. Zustand v5 wraps React's `useSyncExternalStore`, which treats a new array reference as a state change → re-render → selector runs again → new array → infinite loop.

Latent since the Zustand v5 bump (`^5.0.4`). Surfaced consistently in current main; probably required a particular pinned-card state shape to trigger reliably before.

Fix

```ts
// after
import { useShallow } from "zustand/react/shallow";
const pinnedCards = useBoardStore(useShallow((s) => s.pinnedCards()));
```

`useShallow` does a shallow-equality compare on the returned array, so a new reference with the same card elements doesn't trigger a re-render. Canonical Zustand v5 pattern for selectors returning derived collections.

Test plan

• `npm run build` — green
• Window now renders the board instead of blank — confirmed via WebView2 + browser repro
• Manual: open card with pinned items, verify Pinned section renders without crash

🤖 Generated with Claude Code