Add Infinite Query Support for Pagination

## Problem
Current pagination in `useStacSearch` uses next/previous page functions that replace the current results. This doesn't support:
- Infinite scroll UI patterns
- "Load more" buttons
- Accumulating results across pages
- Automatic pagination as user scrolls

Modern STAC viewers need infinite scroll to display large result sets without traditional pagination controls.

## Current Behavior
```typescript
const { results, nextPage, previousPage } = useStacSearch();

// results contains only the current page
// nextPage() replaces results with next page
// Can't accumulate results for infinite scroll
```

## Desired Behavior
```typescript
function InfiniteResults() {
const {
data, // All pages combined
fetchNextPage,
hasNextPage,
isFetchingNextPage,
} = useStacSearchInfinite({
params: { collections: ['landsat-8'] },
});

// Flatten all pages
const allItems = data?.pages.flatMap(page => page.features) ?? [];

return (

## Use Cases from stac-map

stac-map uses `useInfiniteQuery` for both collections and search:

```typescript
// Collections with infinite loading
const collectionsQuery = useInfiniteQuery({
queryKey: ['stac-collections', href],
queryFn: async ({ pageParam }) => fetchCollections(pageParam),
initialPageParam: href,
getNextPageParam: (lastPage) =>
lastPage?.links?.find(link => link.rel === 'next')?.href,
});

// Search with infinite loading
const searchQuery = useInfiniteQuery({
queryKey: ['search', search, link],
initialPageParam: updateLink(link, search),
getNextPageParam: (lastPage) =>
lastPage.links?.find(link => link.rel === 'next'),
queryFn: fetchSearch,
});
```

## Proposed Solution

### Hook Signature
```typescript
type UseStacSearchInfiniteOptions = {
/** Search parameters */
params: StacSearchParams;

/** Optional: specific search link to use */
searchLink?: Link;

/** Enable/disable search */
enabled?: boolean;

/** Custom headers */
headers?: Record;
};

type UseStacSearchInfiniteResult = {
/** All pages of results */
data?: {
pages: SearchResponse[];
pageParams: (Link | undefined)[];
};

/** All items flattened */
items?: Item[];

/** Fetch next page */
fetchNextPage: () => Promise;

/** Fetch previous page (if supported) */
fetchPreviousPage?: () => Promise;

/** Whether there are more pages */
hasNextPage: boolean;
hasPreviousPage?: boolean;

/** Loading states */
isLoading: boolean;
isFetchingNextPage: boolean;
isFetchingPreviousPage?: boolean;

/** Error state */
error?: ApiErrorType;

/** Refetch all pages */
refetch: () => Promise;
};

function useStacSearchInfinite(
options: UseStacSearchInfiniteOptions
): UseStacSearchInfiniteResult;
```

### Implementation
```typescript
import { useInfiniteQuery } from '@tanstack/react-query';
import { useMemo } from 'react';

function useStacSearchInfinite({
params,
searchLink,
enabled = true,
headers = {},
}: UseStacSearchInfiniteOptions): UseStacSearchInfiniteResult {
const { stacApi } = useStacApiContext();

const query = useInfiniteQuery({
queryKey: ['stac-search-infinite', params, searchLink?.href],

queryFn: async ({ pageParam }) => {
if (pageParam) {
// Use pagination link
return await fetchViaLink(pageParam, params);
} else if (stacApi) {
// Initial search via StacApi
const response = await stacApi.search({
...params,
dateRange: params.datetime ? parseDateTime(params.datetime) : undefined,
}, headers);

if (!response.ok) {
throw new ApiError(
response.statusText,
response.status,
await response.text(),
response.url
);
}

return response.json();
} else {
throw new Error('Either provide stacApi context or searchLink');
}
},

initialPageParam: searchLink,

getNextPageParam: (lastPage: SearchResponse) => {
return lastPage.links?.find(link => link.rel === 'next');
},

getPreviousPageParam: (firstPage: SearchResponse) => {
return firstPage.links?.find(link =>
['prev', 'previous'].includes(link.rel)
);
},

enabled: enabled && (!!stacApi || !!searchLink),
retry: false,
});

// Flatten all items from all pages
const items = useMemo(() => {
return query.data?.pages.flatMap(page => page.features) ?? [];
}, [query.data]);

return {
data: query.data,
items,
fetchNextPage: query.fetchNextPage,
fetchPreviousPage: query.fetchPreviousPage,
hasNextPage: query.hasNextPage,
hasPreviousPage: query.hasPreviousPage,
isLoading: query.isLoading,
isFetchingNextPage: query.isFetchingNextPage,
isFetchingPreviousPage: query.isFetchingPreviousPage,
error: query.error,
refetch: query.refetch,
};
}
```

### Example Usage Patterns

#### 1. Infinite Scroll
```typescript
function InfiniteScrollResults() {
const {
items,
fetchNextPage,
hasNextPage,
isFetchingNextPage,
} = useStacSearchInfinite({
params: { collections: ['sentinel-2'], limit: 25 },
});

const observerRef = useRef();

// Intersection observer for automatic loading
useEffect(() => {
const observer = new IntersectionObserver(
(entries) => {
if (entries[0].isIntersecting && hasNextPage && !isFetchingNextPage) {
fetchNextPage();
}
},
{ threshold: 0.1 }
);

if (observerRef.current) {
observer.observe(observerRef.current);
}

return () => observer.disconnect();
}, [hasNextPage, isFetchingNextPage, fetchNextPage]);

return (

Beginne damit, den Einstiegspunkt useStacSearch zu finden und zu prüfen, wie die Paginierung derzeit Ergebnisse ersetzt. Bewerte dann die vorgeschlagene useInfiniteQuery-API, die Seitenakkumulation, die linkbasierte Navigation sowie die Anforderungen an Tests und Dokumentation; abgeschlossen bedeutet, dass die aufgeführten Such- und Collections-Verhaltensweisen abgedeckt sind, ohne die bestehende Paginierung zu ändern.

Vom Indexierungsmodell aus dem Issue-Text verfasst.