Add MCP GetSavedViewWorkItemsTool for filtered queries

What does this MR do and why?

Introduces GetSavedViewWorkItemsTool, a new MCP GraphQL tool that queries namespace.workItems with filters extracted from a saved view. This tool maps saved view filter keys to GraphQL query variables and applies hierarchy scoping defaults.

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

1. GetSavedViewTool (fetch saved view metadata) - !226995 (merged)
2. This MR - GetSavedViewWorkItemsTool (fetch work items with filters)
3. Orchestrator service + tool registration

Key changes

• New Mcp::Tools::WorkItems::GetSavedViewWorkItemsTool class with a GetWorkItemsFull GraphQL query
• Filter mapping from saved view keys to GraphQL variables (assignees, labels, milestones, state, types, confidential, negated/union filters)
• Hierarchy scoping defaults (includeDescendants: true, excludeProjects: false, excludeGroupWorkItems: false)
• Pagination support via first/after params
• Work item response includes widgets (assignees, labels, milestone, dates, hierarchy)
• Comprehensive unit and integration tests

Supported filter mapping

Saved View Filter	GraphQL Variable
assigneeUsernames	$assigneeUsernames
assigneeWildcardId	$assigneeWildcardId
authorUsername	$authorUsername
confidential	$confidential
labelName	$labelName
milestoneTitle	$milestoneTitle
milestoneWildcardId	$milestoneWildcardId
myReactionEmoji	$myReactionEmoji
types	$types
state	$state
not	$not
or	$or

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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