Add meal plan feature with cross-device sync and automatic stale data cleanup

Introduces weekly meal planning with a calendar-based tab view, per-recipe
date assignments synced via Nextcloud Cookbook custom metadata, and 30-day
automatic pruning of old entries on load, save, and sync merge.

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

Nextcloud Cookbook iOS Client/Data/MealPlanModels.swift

@@ -0,0 +1,83 @@
+//
+//  MealPlanModels.swift
+//  Nextcloud Cookbook iOS Client
+//
+
+import Foundation
+
+/// Tracks meal plan assignments for a recipe, stored as `_mealPlanAssignment` in the recipe JSON on the server.
+struct MealPlanAssignment: Codable {
+    var version: Int = 1
+    var lastModified: String
+    var dates: [String: MealPlanDateEntry]
+
+    init(lastModified: String = MealPlanDate.now(), dates: [String: MealPlanDateEntry] = [:]) {
+        self.version = 1
+        self.lastModified = lastModified
+        self.dates = dates
+    }
+}
+
+struct MealPlanDateEntry: Codable {
+    enum Status: String, Codable {
+        case assigned
+        case removed
+    }
+
+    var status: Status
+    var mealType: String?
+    var modifiedAt: String
+
+    init(status: Status, mealType: String? = nil, modifiedAt: String = MealPlanDate.now()) {
+        self.status = status
+        self.mealType = mealType
+        self.modifiedAt = modifiedAt
+    }
+}
+
+/// ISO 8601 date helpers for meal plan dates.
+enum MealPlanDate {
+    private static let isoFormatter: ISO8601DateFormatter = {
+        let f = ISO8601DateFormatter()
+        f.formatOptions = [.withInternetDateTime]
+        return f
+    }()
+
+    private static let dayFormatter: DateFormatter = {
+        let f = DateFormatter()
+        f.dateFormat = "yyyy-MM-dd"
+        f.timeZone = .current
+        return f
+    }()
+
+    static func now() -> String {
+        isoFormatter.string(from: Date())
+    }
+
+    static func date(from string: String) -> Date? {
+        isoFormatter.date(from: string)
+    }
+
+    static func string(from date: Date) -> String {
+        isoFormatter.string(from: date)
+    }
+
+    static func dayString(from date: Date) -> String {
+        dayFormatter.string(from: date)
+    }
+
+    static func dateFromDay(_ dayString: String) -> Date? {
+        dayFormatter.date(from: dayString)
+    }
+}
+
+/// Local-only aggregated view struct used by the UI.
+struct MealPlanEntry: Identifiable {
+    let recipeId: String
+    let recipeName: String
+    let date: Date
+    let dateString: String
+    let mealType: String?
+
+    var id: String { "\(recipeId)-\(dateString)" }
+}