feat: add project updates and expose projectId in bulk updates

[athal7]

Summary

This PR adds two features:

1. New linear_create_project_update tool - Create project updates (status reports) in Linear to communicate project progress and health status
2. Expose projectId in linear_bulk_update_issues - Allow assigning/removing issues from projects during bulk updates

Feature 1: Create Project Updates

Add support for creating project updates (status reports) in Linear.

Changes

• Add ProjectUpdateCreateInput, ProjectUpdate, and ProjectUpdateCreateResponse types
• Add CREATE_PROJECT_UPDATE_MUTATION GraphQL mutation
• Add createProjectUpdate method to LinearGraphQLClient
• Add linear_create_project_update tool schema with projectId (required), body (optional), and health (optional) parameters
• Add handleCreateProjectUpdate handler to ProjectHandler
• Add comprehensive unit tests covering all health statuses and error cases

Usage

// Create a project update with health status
{
  projectId: "project-id-here",
  body: "We're on track for Q1 delivery. All milestones met.",
  health: "onTrack"  // or "atRisk" (yellow) or "offTrack" (red)
}

// Minimal update (just project ID)
{
  projectId: "project-id-here"
}

Feature 2: Set Issue Project via Bulk Update

Expose projectId parameter in linear_bulk_update_issues tool schema.

Changes

• Add projectId property to the update object in linear_bulk_update_issues schema
• Add test for updating issue project assignment

Usage

// Assign issues to a project
{
  issueIds: ["issue-1", "issue-2"],
  update: {
    projectId: "project-id-here"
  }
}

Testing

All existing tests pass, plus 6 new tests for the added functionality.