feat(nimbus): Add Rollout Schedule Card

[RJAK11]

Because

• We need to be able to manage rollout schedules from the rollout summary page

This commit

• Adds a rollout schedule card with phase dates and population percentages
• Adds support for adding and removing rollout phases
• Shows rollout phase progress with ability to pause/resume/start buttons

Fixes #15081

Screen.Recording.2026-06-22.at.10.28.23.AM.mov

Screen.Recording.2026-06-22.at.11.41.37.AM.mov

schedule.demo.mp4

[moibra05]

found a couple bugs testing locally:

• its possible to set only the start or end date without the other. im not sure if this is intentional
• deleting/adding a phase then cancelling the form does not undo the phase action

besides that i think the code looks really good to me :)

[yashikakhurana]

Thank you @RJAK11 this is great, overall looks good, just some design changes

we will move all the controls like start phase etc etc left side on the sidebar, so this start here will not required

[RJAK11]

Thank you both for the reviews! I have addressed all the mentioned issues and you can see the changes in the video. For the bug regarding deleting/adding a phase then cancelling the form not undoing the action, I initially avoided that to prevent introducing some complicated code but I just added it with the other changes. Let me know if this approach looks okay or if you think there’s a better way to handle it 🙏🏼

Screen.Recording.2026-06-25.at.11.14.20.AM.mov

[yashikakhurana]

In general looks good, thank you @RJAK11, some suggestion, some views and urls are not needed now as we are not adding pause/start here