Initiales HabitTracker-Projekt: SwiftUI + SwiftData Gewohnheiten-Tracker

Natives iOS-App-Gerüst (Xcode 26, synchronisierte Ordner, iOS 18+).

Features:
- Gewohnheiten anlegen (Name, SF-Symbol, Farbe), heute abhaken, Streaks, Löschen
- Detailansicht mit Monatskalender (Tage nachtragbar) und Statistiken
- Tägliche Erinnerungen via lokale Notifications
- Home-Screen-Widget (klein/mittel) mit App-Group-Datenaustausch

HabitTracker/Models/Habit.swift

@@ -0,0 +1,84 @@
+import Foundation
+import SwiftData
+
+@Model
+final class Habit {
+    var uuid: UUID = UUID()
+    var name: String
+    var symbolName: String
+    var colorHex: String
+    var createdAt: Date
+    /// Time of day for the daily reminder; nil means no reminder.
+    var reminderTime: Date?
+
+    @Relationship(deleteRule: .cascade, inverse: \HabitEntry.habit)
+    var entries: [HabitEntry] = []
+
+    init(
+        name: String,
+        symbolName: String = "star.fill",
+        colorHex: String = "#34C759",
+        createdAt: Date = .now,
+        reminderTime: Date? = nil
+    ) {
+        self.name = name
+        self.symbolName = symbolName
+        self.colorHex = colorHex
+        self.createdAt = createdAt
+        self.reminderTime = reminderTime
+    }
+}
+
+extension Habit {
+    /// Whether this habit was checked off on the given day.
+    func isCompleted(on day: Date, calendar: Calendar = .current) -> Bool {
+        entries.contains { calendar.isDate($0.date, inSameDayAs: day) }
+    }
+
+    var isCompletedToday: Bool {
+        isCompleted(on: .now)
+    }
+
+    /// Number of consecutive days (counting back from today) the habit was done.
+    var currentStreak: Int {
+        let calendar = Calendar.current
+        let doneDays = Set(entries.map { calendar.startOfDay(for: $0.date) })
+        var day = calendar.startOfDay(for: .now)
+
+        // A streak stays alive if today isn't done yet but yesterday was.
+        if !doneDays.contains(day) {
+            day = calendar.date(byAdding: .day, value: -1, to: day)!
+        }
+
+        var streak = 0
+        while doneDays.contains(day) {
+            streak += 1
+            day = calendar.date(byAdding: .day, value: -1, to: day)!
+        }
+        return streak
+    }
+
+    /// Longest run of consecutive completed days, ever.
+    var longestStreak: Int {
+        let calendar = Calendar.current
+        let days = Set(entries.map { calendar.startOfDay(for: $0.date) }).sorted()
+        guard !days.isEmpty else { return 0 }
+
+        var longest = 1
+        var run = 1
+        for i in 1..<days.count {
+            let expectedPrev = calendar.date(byAdding: .day, value: -1, to: days[i])!
+            if calendar.isDate(expectedPrev, inSameDayAs: days[i - 1]) {
+                run += 1
+            } else {
+                run = 1
+            }
+            longest = max(longest, run)
+        }
+        return longest
+    }
+
+    var totalCompletions: Int {
+        entries.count
+    }
+}