Fix critical GraphQL syntax errors that occur when client directives (@SInCE, @deprecatedSince, @skipOnClient) remove all fields from fragments, leaving empty fragment definitions and orphaned fragment spreads.

Background/Purpose

The current GraphQL transformer implementation has a critical bug where client directives that remove all fields from fragments create invalid GraphQL syntax. This causes two types of errors:

1. Empty fragment definitions without selection sets (e.g., fragment AgentStatsFragment on Query)
2. Fragment spreads referencing non-existent fragments (e.g., ...AgentStatsFragment when the fragment was removed)

These errors break GraphQL query execution in components like DashboardPage when backend versions don't support certain features.

Acceptance Criteria

• GraphQL transformer properly handles fragments emptied by client directives
• No syntax errors when client directives remove all fragment fields
• No "Unknown fragment" errors for orphaned fragment spreads
• Generated GraphQL queries remain valid and executable
• Maintains backward compatibility with existing functionality

Technical Impact

• Prevents runtime GraphQL errors in production
• Improves robustness of client-side query transformation
• Ensures proper version compatibility handling

JIRA Issue: FR-1663