Add stream milestone notifications at 25%, 50%, and 75% completion on the detail page

[Chuks-coderr]

Overview

Recipients watching a long-running vesting stream want to be notified when it passes key completion milestones. Visual milestone markers and browser notifications at 25%, 50%, and 75% would provide this.

Problem

There are no completion milestone markers on the stream detail page. Users must manually check the percentage complete to notice key thresholds passing.

Proposed Solution

• Add milestone markers at 25%, 50%, and 75% on the stream progress bar
• When the claimable ticker crosses a milestone, show a toast notification
• Each milestone fires once per stream per session
• Opt-in browser push notification for milestones when the tab is not active

Acceptance Criteria

• Milestone markers visible at 25%, 50%, and 75% on the progress bar
• Toast fired once per milestone crossing per session
• Browser push notification opt-in available on the stream detail page
• No duplicate toasts if the page re-renders at the same percentage