[WIP] Friends PR-3: Friends management UI

[brelieu05]

Summary

Adds the Manage Friends UI as a centered dialog from the header Friends button. This replaces the old FriendScheduleEntry popover with a full friends list and friend-request management flow.

Test plan

• Sign out → click Friends → sign-in dialog appears
• Sign in → Friends dialog opens with Friends and Requests tabs
• Friends tab: search filters the list; View opens the friend schedule dialog; unfriend flow works and refreshes the list
• Requests tab: send a request by email; accept/reject received requests; cancel sent requests
• Leave dialog open and confirm list updates after actions on another device/session
• Verify layout on mobile (icon button) and desktop (Friends text button)
• Check dark mode styling for tabs, search fields, and friend cards

Issues

Closes #

Depends on #1856

[cubic-dev-ai]

No issues found across 13 files

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