Add MCP GetSavedViewTool for fetching saved views

What does this MR do and why?

Introduces GetSavedViewTool, a new MCP GraphQL tool that queries namespace.savedViews to retrieve a saved view's metadata (name, description, filters, and sort configuration).

This is the first of three MRs that break down !226663 (closed):

1. This MR - GetSavedViewTool (fetch saved view metadata)
2. GetSavedViewWorkItemsTool (fetch work items with filters)
3. Orchestrator service + tool registration

Key changes

• New Mcp::Tools::WorkItems::GetSavedViewTool class that builds and executes a GetNamespaceSavedView GraphQL query
• Extracts the first saved view node from the response and returns it as structured content
• Returns an error if the saved view is not found or the user lacks access
• Comprehensive unit and integration tests

How to set up and validate locally

Unit tests have been added. UI tests will be shared in the third MR.

References

• Part of #592440
• Split from !226663 (closed)
• Implementation follows the MCP GraphQL Integration design document

MR acceptance checklist

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