(#50) Implement pinned action pane and DOW fix

[bfalls]

Fixes #50

• Defaulted new alarms to start with no repeat days selected while preserving saved recurrence for existing alarms.
• Restructured the alarm editor sheet into a scrollable form with a pinned bottom action pane that includes a divider, navigation bar padding, and a text-based Cancel control while keeping existing delete/duplicate/save behaviors.