Problem There's no way to display milestones that apply across the entire Gantt independent of the task hierarchy. Tying milestones to task rows means they disappear when rows collapse, and sibling-row workarounds are visually indistinguishable from real content rows.

Requested Behavior A pinned milestone band rendered above the task rows, below the timeline header, that:

• Stays visible regardless of row collapse state
• Scrolls horizontally with the timeline but not vertically with tasks
• Accepts milestone objects with date, label, color, and type
• Supports multiple milestones on the same band (stagger or tooltip on hover)

Use Case In our publication planning workflow, study-level dates (Data Lock, Embargo Lift, Interim Analysis) are reference points that need to be visible while scrolling through 20–50 task rows. These don't belong to any single task — they're plan-wide context.

Proposed API

globalMilestones: [
  { date: new Date("2026-03-01"), label: "Data Lock", color: "#F58010" },
  { date: new Date("2026-05-15"), label: "Embargo Lift", color: "#20B34A" },
],
showGlobalMilestoneBand: true,
globalMilestoneBandHeight: 32