[Enh]: New pagination keywords

## Existing, unchanged keywords

* `$first`: return the first N items, similar to SQL `TOP`.
* `$after`: return items after this cursor; not offset-based.

## New keywords

* `$pageSize`: number of records per page
* `$pageNumber`: numeric page index (1-based)

### Default behavior

* `$pageSize` defaults to the configured DAB `page-size` value if not specified.
* `$pageNumber` defaults to `1` if not specified.

### Evaluation precedence

`$after → $pageSize → $pageNumber → $first`

They can all be used together.

## Keywords not being added

I include this section of the specification because these keywords were part of previous conversations and specifications. However, we are not going to add them anymore because they are redundant.

* `$take`: semantically identical to `$first`.
* `$skip`: semantically equivalent to `$pageSize` + `$pageNumber`. For example, `$skip=10` can be expressed as `$pageSize=5` and `$pageNumber=3`. Skip behavior can also be achieved using `$after`, optionally combined with `$first`.

## Examples in TSQL

```sql
-- Example 1: All parameters NULL (no paging applied)

DECLARE @First int = NULL;
DECLARE @After int = NULL;
DECLARE @PageSize int = NULL;
DECLARE @PageNumber int = NULL;

SELECT *
FROM dbo.Actor
ORDER BY Id;
```

```sql
-- Example 2: Page model ($pageSize + $pageNumber)
-- DAB requests PageSize + 1 to determine NextLink

DECLARE @First int = NULL;
DECLARE @After int = NULL;
DECLARE @PageSize int = 5;
DECLARE @PageNumber int = 3;

SELECT *
FROM dbo.Actor
ORDER BY Id
OFFSET (@PageNumber - 1) * @PageSize ROWS
FETCH NEXT (@PageSize + 1) ROWS ONLY;
```

```sql
-- Example 3: $pageSize only (defaults pageNumber = 1)
-- DAB fetches PageSize + 1 for NextLink detection

DECLARE @First int = NULL;
DECLARE @After int = NULL;
DECLARE @PageSize int = 5;
DECLARE @PageNumber int = NULL;

SET @PageNumber = ISNULL(@PageNumber, 1);

SELECT *
FROM dbo.Actor
ORDER BY Id
OFFSET (@PageNumber - 1) * @PageSize ROWS
FETCH NEXT (@PageSize + 1) ROWS ONLY;
```

```sql
-- Example 4: Cursor model ($first only)
-- DAB fetches First + 1 for NextLink detection

DECLARE @First int = 5;
DECLARE @After int = NULL;
DECLARE @PageSize int = NULL;
DECLARE @PageNumber int = NULL;

SELECT TOP (@First + 1) *
FROM dbo.Actor
ORDER BY Id;
```

```sql
-- Example 5: Cursor model ($first + $after)
-- DAB fetches First + 1 for NextLink detection

DECLARE @First int = 5;
DECLARE @After int = 10; -- simplified for this example
DECLARE @PageSize int = NULL;
DECLARE @PageNumber int = NULL;

SELECT TOP (@First + 1) *
FROM dbo.Actor
WHERE Id > @After
ORDER BY Id;
```

```sql
-- Example 6: $after + $pageSize
-- DAB fetches PageSize + 1 for NextLink detection

DECLARE @First int = NULL;
DECLARE @After int = 10; -- simplified for this example
DECLARE @PageSize int = 5;
DECLARE @PageNumber int = NULL;

SELECT TOP (@PageSize + 1) *
FROM dbo.Actor
WHERE Id > @After
ORDER BY Id;
```

```sql
-- Example 7: $first + $pageSize + $pageNumber
-- Page window fetches PageSize + 1
-- Final limiter applies after trimming NextLink row

DECLARE @First int = 2;
DECLARE @After int = NULL;
DECLARE @PageSize int = 5;
DECLARE @PageNumber int = 3;

WITH Paged AS
(
SELECT *
FROM dbo.Actor
ORDER BY Id
OFFSET (@PageNumber - 1) * @PageSize ROWS
FETCH NEXT (@PageSize + 1) ROWS ONLY
)
SELECT TOP (@First)
*
FROM Paged
ORDER BY Id;
```

```sql
-- Example 8: ⛔ Incompatible: $after + $pageNumber

DECLARE @First int = NULL;
DECLARE @After int = 10; -- simplified for this example
DECLARE @PageSize int = NULL;
DECLARE @PageNumber int = 2;

IF @After IS NOT NULL AND @PageNumber IS NOT NULL
THROW 50000, '$after cannot be combined with $pageNumber.', 1;
```

```sql
-- Example 9: ⛔ Invalid: $pageNumber without $pageSize

DECLARE @First int = NULL;
DECLARE @After int = NULL;
DECLARE @PageSize int = NULL;
DECLARE @PageNumber int = 2;

IF @PageNumber IS NOT NULL AND @PageSize IS NULL
THROW 50000, '$pageNumber requires $pageSize.', 1;
```

```sql
-- Example 10: ⛔ Invalid negative values

DECLARE @First int = -5;
DECLARE @After int = NULL;
DECLARE @PageSize int = -10;
DECLARE @PageNumber int = NULL;

IF @First IS NOT NULL AND @First <= 0
THROW 50000, '$first must be greater than zero.', 1;

IF @PageSize IS NOT NULL AND @PageSize <= 0
THROW 50000, '$pageSize must be greater than zero.', 1;
```

Beginne damit nachzuverfolgen, wie DAB derzeit die vorhandenen Schlüsselwörter $first und $after auswertet und wie der konfigurierte Seitengrößenwert angewendet wird. Verwende die T-SQL-Beispiele als Verhaltensfälle, einschließlich Priorität, Standardwerten, ungültigen Kombinationen und negativen Werten. Als erledigt gilt die Aufgabe, wenn $pageSize und $pageNumber mit den angegebenen Kombinationen funktionieren und dabei das bestehende Verhalten der Schlüsselwörter sowie die Erkennung von NextLink erhalten bleiben.

Vom Indexierungsmodell aus dem Issue-Text verfasst.