[Bug]: GraphQL schema fails to initialize when stored procedure parameter defaults use non-numeric strings

When a stored procedure entity defines parameter defaults using non-numeric strings (for example `"default": "number"`), Data API builder fails to start with GraphQL enabled. The service throws a `DataApiBuilderException` during schema generation and `/graphql` becomes unavailable.

**Steps to Reproduce:**

1. Define a stored procedure entity like this:

```json
"GetSeriesActors": {
"source": {
"object": "dbo.GetSeriesActors",
"type": "stored-procedure",
"parameters": [
{ "name": "seriesId", "required": false, "default": "number" },
{ "name": "top", "required": false, "default": "number" }
]
},
"graphql": { "enabled": true, "operation": "mutation" }
}
```
2. Start DAB with GraphQL enabled.
3. Observe logs.

**Expected Behavior:**
DAB should either:

* Treat `"default": "number"` as a literal string value, or
* Reject invalid defaults during configuration validation with a clear error message before startup.

**Actual Behavior:**
DAB starts but fails when GraphQL initializes. The logs show:

```
DataApiBuilderException: The parameter value number provided in configuration cannot be converted to the type Int
System.FormatException: The input string 'number' was not in a correct format.
at System.Int32.Parse(String s)
```

After this error, `/graphql` is unavailable, though REST endpoints continue to function normally.

**Environment:**

* Data API builder version: 1.7.75
* Database: SQL Server
* Host: Azure Container Apps
* Authentication: StaticWebApps

**Notes:**
The exception originates from `GraphQLStoredProcedureBuilder.ConvertValueToGraphQLType` when attempting to parse the invalid default value. DAB should validate or sanitize stored procedure parameter defaults before GraphQL schema generation to prevent this runtime failure.

まず、GraphQL を有効にした stored-procedure の構成を再現し、報告された変換失敗が発生する GraphQLStoredProcedureBuilder.ConvertValueToGraphQLType を調査します。無効な文字列のデフォルト値によって GraphQL スキーマの初期化が妨げられなくなったことを、これらをリテラル値として扱うか、起動前に明確な構成エラーを生成することで確認します。

索引モデルが issue の本文から書いたものです。