Fix watchOS CI compile for proactive notification type

[cortexark]

Summary

• move ProactiveNotificationType into Shared so both iOS and watchOS targets can compile it
• remove duplicate iOS-only enum declaration from ProactiveNotificationService

Why

CI run 24158584293 failed at Build watchOS because Shared/Services/ProactiveNotificationStore referenced ProactiveNotificationType that only existed in an iOS-only file.

Validation

• xcodebuild build -project Thump.xcodeproj -scheme ThumpWatch -destination "generic/platform=watchOS Simulator" -configuration Debug CODE_SIGN_IDENTITY="" CODE_SIGNING_REQUIRED=NO
• xcodebuild build -project Thump.xcodeproj -scheme Thump -destination "generic/platform=iOS Simulator" -configuration Debug CODE_SIGN_IDENTITY="" CODE_SIGNING_REQUIRED=NO