feat: Add calendar/Gantt view for visualizing vesting schedules

[Austinaminu2]

Description

Users managing multiple streams (e.g., a company running payroll or a DAO distributing grants) need a way to see all their vesting schedules at a glance. A calendar or Gantt-style timeline view would show:

• When each stream starts and ends
• Cliff dates highlighted
• Overlap between multiple streams
• Current position (today marker)

Proposed Solution

Add a new view toggle on the dashboard/streams page:

• List view (current default)
• Timeline view (new)

The timeline should be horizontal, with time on the X-axis and one row per stream. Color-code by status (active = green, completed = gray, cancelled = red).

Acceptance Criteria

• Toggle between list and timeline views on the streams page
• Each stream renders as a horizontal bar from start to end time
• Cliff dates shown as vertical markers within each bar
• "Today" line clearly visible across all streams
• Tooltip on hover shows stream details (amount, recipient, % unlocked)
• Responsive — collapses gracefully on mobile
• Persists view preference in localStorage