Replace TipKit with custom themed tips modal system

- Add TipModalView with gradient header, themed styling, and spring animations
- Create FeelsTipsManager with global toggle, session tracking, and persistence
- Define FeelsTip protocol and convert all 7 tips to new system
- Add convenience view modifiers (.customizeLayoutTip(), .aiInsightsTip(), etc.)
- Remove TipKit dependency from all views
- Add Tips Preview debug screen in Settings to test all tip modals
- Update documentation for new custom tips system

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Shared/Views/DayView/DayView.swift

@@ -7,7 +7,6 @@
 
 import SwiftUI
 import SwiftData
-import TipKit
 
 struct DayViewConstants {
     static let maxHeaderHeight = 200.0