Fix beta Security OpenAPI schemas generating undefined C# types

Problem

The refreshed beta Security OpenAPI document contains two free-form object schemas that AutoREST.PowerShell generates as the invalid C# type undefined.undefined:

1. microsoft.graph.security.securityCopilot.prompt.inputs
   • References microsoft.graph.Dictionary.
   • microsoft.graph.Dictionary is defined as type: object with additionalProperties: { type: object }.
2. microsoft.graph.security.detectionAction.responseActions[]
   • References microsoft.graph.security.responseAction.
   • microsoft.graph.security.responseAction is an empty type: object with additionalProperties: { type: object }.

The generated beta Security module fails C# compilation with errors such as:

error CS0246: The type or namespace name 'undefined' could not be found

Affected generated models include:

• MicrosoftGraphSecurityCopilotPrompt
• MicrosoftGraphSecurityDetectionAction

Required OpenAPI correction

Update these schemas to use concrete, generator-supported types. If these values are intentionally arbitrary JSON, model them using the supported free-form object representation rather than an object whose values are themselves untyped objects. The exact schema should reflect the API contract for:

• Security Copilot prompt input values
• Custom detection response actions

Temporary SDK workaround

PR #3701 removes only these two properties from AutoREST's in-memory OpenAPI document using directives in src/Security/Security.md:

• microsoft.graph.security.securityCopilot.prompt.inputs
• microsoft.graph.security.detectionAction.responseActions

This preserves the associated endpoints and other model properties while allowing beta Security generation and compilation to complete.

Completion criteria

• Correct both schemas in the source OpenAPI transforms.
• Confirm AutoREST.PowerShell generates valid C# types for both properties.
• Remove the temporary property-removal directives from src/Security/Security.md.
• Regenerate and build the beta Security module successfully.

Related: #3701

Start by locating the source OpenAPI transforms for the securityCopilot.prompt.inputs and detectionAction.responseActions schemas, then compare them with the generator-supported free-form object representation. Regenerate and build the beta Security module to confirm valid C# types, and remove the temporary property-removal directives from src/Security/Security.md.