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/FeelsApp.swift

@@ -9,7 +9,6 @@ import SwiftUI
 import SwiftData
 import BackgroundTasks
 import WidgetKit
-import TipKit
 
 @main
 struct FeelsApp: App {
@@ -30,8 +29,8 @@ struct FeelsApp: App {
         }
         UNUserNotificationCenter.current().setBadgeCount(0)
 
-        // Configure TipKit
-        TipsManager.shared.configure()
+        // Reset tips session on app launch
+        FeelsTipsManager.shared.resetSession()
 
         // Initialize Live Activity scheduler
         LiveActivityScheduler.shared.scheduleBasedOnCurrentTime()