Expand ALL permissions in MCP describe_entities to explicit operations (#2951)

The MCP `describe_entities` tool returns `"ALL"` for wildcard
permissions, which confuses LLM consumers that need explicit operation
lists.

### Changes

Modified `DescribeEntitiesTool.BuildPermissionsInfo()` to expand
`EntityActionOperation.All`:
- **Tables/Views**: Expands to `["CREATE", "DELETE", "READ", "UPDATE"]`
via `EntityAction.ValidPermissionOperations`
- **Stored Procedures**: Expands to `["EXECUTE"]` via
`EntityAction.ValidStoredProcedurePermissionOperations`

### Example

**Before:**
```json
{
  "name": "Todo",
  "permissions": ["ALL"]
}
```

**After:**
```json
{
  "name": "Todo",
  "permissions": ["CREATE", "DELETE", "READ", "UPDATE"]
}
```

<!-- START COPILOT CODING AGENT SUFFIX -->



<details>

<summary>Original prompt</summary>

> 
> ----
> 
> *This section details on the original issue you should resolve*
> 
> <issue_title>[Bug]: MCP `describe_entities` permissions value `ALL`
needs to be expanded.</issue_title>
> <issue_description>## What? 
> 
> Models are confused by `ALL`.
> 
> ```json
> {
>   "entities": [
>     {
>       "name": "Todo",
>       "description": "This table contains the list of todo items.",
>       "fields": [ ],
>       "permissions": [
>         "ALL" // this is the problem
>       ]
>     }
>   ],
>   "count": 1,
>   "mode": "full",
>   "status": "success"
> }
> ```
> 
> ## Solution
> 
> When table/view.
> 
> ```json
> {
>   "permissions: [
>     "CREATE",
>     "DELETE",
>     "READ",
>     "UPDATE"
>   ]
> }
> ```
> 
> When stored procedure.
> 
> ```json
> {
>   "permissions: [
>     "EXECUTE"
>   ]
> }
> ```
> </issue_description>
> 
> ## Comments on the Issue (you are @copilot in this section)
> 
> <comments>
> </comments>
> 


</details>

- Fixes #2935

---------

Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: JerryNixon <[email protected]>

Author: 3 people

src/Azure.DataApiBuilder.Mcp/BuiltInTools/DescribeEntitiesTool.cs

@@ -368,13 +368,30 @@ private static List<object> BuildParameterMetadataInfo(List<ParameterMetadata>?
         /// <returns>A list of permissions available to the entity</returns>
         private static string[] BuildPermissionsInfo(Entity entity)
         {
-            HashSet<string> permissions = new();
+            if (entity.Permissions == null)
+            {
+                return Array.Empty<string>();
+            }
+
+            bool isStoredProcedure = entity.Source.Type == EntitySourceType.StoredProcedure;
+            HashSet<EntityActionOperation> validOperations = isStoredProcedure
+                ? EntityAction.ValidStoredProcedurePermissionOperations
+                : EntityAction.ValidPermissionOperations;
 
-            if (entity.Permissions != null)
+            HashSet<string> permissions = new(StringComparer.OrdinalIgnoreCase);
+
+            foreach (EntityPermission permission in entity.Permissions)
             {
-                foreach (EntityPermission permission in entity.Permissions)
+                foreach (EntityAction action in permission.Actions)
                 {
-                    foreach (EntityAction action in permission.Actions)
+                    if (action.Action == EntityActionOperation.All)
+                    {
+                        foreach (EntityActionOperation op in validOperations)
+                        {
+                            permissions.Add(op.ToString().ToUpperInvariant());
+                        }
+                    }
+                    else
                     {
                         permissions.Add(action.Action.ToString().ToUpperInvariant());
                     }