.NET: Hyperlight host-tool parameter schemas missing from execute_code descriptions

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## Parent issue

Sub-issue of #8125. Sibling #8445 is separate and must not close this child or the parent.

## Confirmed behavior

At upstream/main `999dda7970fe969c0901d524365ce34ecbda6227`, `dotnet/src/Microsoft.Agents.AI.Hyperlight/Internal/InstructionBuilder.cs::BuildExecuteCodeDescription` emits each host `AIFunction` name and description but never reads `JsonSchema`. The model therefore does not receive host-tool parameter names, requiredness, descriptions, enums, or nested shapes through this listing.

Both `HyperlightExecuteCodeFunction` and `HyperlightCodeActProvider` use this shared builder. Inspect the standalone function Description or the provider-returned execute-code function description; current BuildInstructions() returns short guidance and is not the correct reproduction accessor.

## Acceptance criteria

- Surface existing host-tool parameter schemas in the model-facing execute-code description for both entry points.
- Add parameterized-host-tool regression coverage; the current builder test uses a zero-parameter function and misses the defect.
- Preserve no-tool output, the code-only execute-code input schema, approval behavior, filesystem host-path protection, and network restrictions.
- Keep the fix focused and document directly affected behavior. Confirm rendering and public API choices separately.

## Status

Deferred at the user request and outside the sibling PR. This child does not authorize implementation. Source behavior was independently confirmed; no new build or live-model reproduction was run. The parent includes a contributor offer to help, so coordinate ownership and check for an implementing PR before starting.

Start in dotnet/src/Microsoft.Agents.AI.Hyperlight/Internal/InstructionBuilder.cs at BuildExecuteCodeDescription, then inspect HyperlightExecuteCodeFunction and HyperlightCodeActProvider and the existing builder test. Verify the standalone and provider-returned descriptions with a parameterized host tool. Done means schemas are surfaced while the listed no-tool, input-schema, approval, filesystem, and network behaviors remain unchanged.

Written by the indexing model from the issue text.