DATA-2: optional list params + normalize frontend's '==' Gridify operator

- GridifyParams wrapper: nullable page/pageSize/filter/orderBy so list endpoints
  work with no query params (Gridify's non-nullable int Page made [AsParameters]
  treat them as required -> 400). Defaults page=1,pageSize=20.
- Normalize incoming filter '==' -> '=' : the frontend gridify.ts emits '==' for
  equals (its convention) but Gridify's equals is '='. Safe (values are escaped;
  != >= <= =* contain no '=='). Fixes status==Active (frontend default that 500'd).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

GerbilManagerWebAPI/Common/PagedResult.cs

@@ -6,22 +6,49 @@ namespace GerbilManagerWebAPI.Common
     /// <summary>Standard paged list envelope returned by every list endpoint.</summary>
     public record PagedResult<T>(IReadOnlyList<T> Items, int TotalCount, int Page, int PageSize);
 
+    /// <summary>
+    /// Query-string parameters for list endpoints. All optional (nullable) so the
+    /// frontend can call a list with no params; Gridify's own GridifyQuery has
+    /// non-nullable int Page/PageSize which [AsParameters] would make REQUIRED.
+    /// Bound via [AsParameters]: ?filter=…&orderBy=…&page=1&pageSize=20.
+    /// </summary>
+    public class GridifyParams
+    {
+        public string? Filter { get; set; }
+        public string? OrderBy { get; set; }
+        public int? Page { get; set; }
+        public int? PageSize { get; set; }
+
+        public GridifyQuery ToQuery() => new()
+        {
+            Filter = NormalizeFilter(Filter),
+            OrderBy = OrderBy,
+            Page = Page is > 0 ? Page.Value : 1,
+            PageSize = PageSize is > 0 ? PageSize.Value : 20,
+        };
+
+        // The frontend's gridify.ts emits "==" for equals (its documented convention),
+        // but Gridify's equals operator is a single "=". Translate "==" -> "=". This is
+        // safe because the frontend backslash-escapes any "=" inside values, and the
+        // other operators it uses ( != >= <= =* ) contain no literal "==".
+        private static string? NormalizeFilter(string? filter) =>
+            string.IsNullOrEmpty(filter) ? filter : filter.Replace("==", "=");
+    }
+
     public static class QueryableExtensions
     {
         /// <summary>
         /// Apply a Gridify query (filter/order/page) to an EF query and project each
         /// row to a DTO, returning the standard paged envelope. Filter/orderBy names
         /// are the ENTITY property names (case-insensitive), e.g. "status==Active",
-        /// "orderBy=dateOfBirth", "litterId==...".
+        /// "orderBy=dateOfBirth", "litterId==…".
         /// </summary>
         public static async Task<PagedResult<TDto>> ToPagedResultAsync<TEntity, TDto>(
             this IQueryable<TEntity> source,
-            GridifyQuery query,
+            GridifyParams parameters,
             Func<TEntity, TDto> map)
         {
-            query.Page = query.Page <= 0 ? 1 : query.Page;
-            query.PageSize = query.PageSize <= 0 ? 20 : query.PageSize;
-
+            var query = parameters.ToQuery();
             Paging<TEntity> paging = await source.GridifyAsync(query);
             var items = paging.Data.Select(map).ToList();
             return new PagedResult<TDto>(items, paging.Count, query.Page, query.PageSize);