Move month, milestone, "include private", and "show labels" settings to global application level

Description

Currently, month, milestone, "include private", and "show labels" settings appear to be configured per individual chart. This creates inconsistent user experience and requires repetitive configuration. These settings should be moved to a global application level where they apply uniformly across all charts and visualizations.

User Story

As a user analyzing my GitLab data, I want to set my preferences for time period, milestone filter, privacy settings, and label visibility once at the application level, so that all charts consistently reflect the same parameters without requiring individual configuration.

Current State Issues

• Inconsistent settings across different charts
• Repetitive configuration for each visualization
• Risk of comparing charts with different parameters
• Poor user experience with scattered controls