v0.6.0 — Phase β-5 Marketplace

Voller Marketplace-Flow mit TabBar und Universal-Link-Handler.
Drei Live-Decks (Geografie, English A2, Periodensystem) sind
browse-, abonnier- und lernbar.

- PublicDeckEntry/PublicDeck/PublicDeckVersion/PublicDeckOwner/
  PublicDeckDetail Codable mit snake_case
- ExploreResponse, BrowseResponse, SubscribeResponse
- MarketplaceSort-Enum (recent/popular/trending)
- CardsAPI.explore/browseMarketplace/publicDeck/subscribe/unsubscribe
- MarketplaceStore @Observable mit Explore + Browse States
- ExploreView: Featured + Trending Horizontal-Carousels, Browse-Link
- BrowseView: Searchable + Sort-Picker + List
- PublicDeckView: Header/Metadata/Subscribe — Subscribe löst Auto-Fork
  serverseitig aus, Response liefert private_deck_id, NavigationLink
  zum eigenen Deck
- PublicDeckCard + BrowseRow mit forest-Theme
- RootView: TabBar (Decks/Entdecken/Account) statt Single-View
- Universal-Link-Handler: onOpenURL + onContinueUserActivity für
  https://cardecky.mana.how/d/<slug> und cards://d/<slug>
- associated-domains: applinks:cardecky.mana.how im entitlement
- 5 neue Marketplace-Decoding-Tests (35 Total grün)

Universal-Links funktionieren erst nach AASA-Setup auf
cardecky.mana.how/.well-known/apple-app-site-association
(Web-Aufgabe, heute 404).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Sources/Features/Marketplace/MarketplaceStore.swift

@@ -0,0 +1,56 @@
+import Foundation
+import ManaCore
+import Observation
+
+/// Holt Explore-Daten und Browse-Resultate. Browse hat einen aktuellen
+/// Query-/Sort-State; bei Änderung wird neu gefetcht.
+@MainActor
+@Observable
+final class MarketplaceStore {
+    private(set) var featured: [PublicDeckEntry] = []
+    private(set) var trending: [PublicDeckEntry] = []
+    private(set) var browseResults: [PublicDeckEntry] = []
+    private(set) var isLoadingExplore = false
+    private(set) var isLoadingBrowse = false
+    private(set) var errorMessage: String?
+
+    var browseQuery: String = ""
+    var browseSort: MarketplaceSort = .recent
+    var browseLanguage: String?
+
+    private let api: CardsAPI
+
+    init(auth: AuthClient) {
+        api = CardsAPI(auth: auth)
+    }
+
+    func loadExplore() async {
+        isLoadingExplore = true
+        errorMessage = nil
+        defer { isLoadingExplore = false }
+        do {
+            let res = try await api.explore()
+            featured = res.featured
+            trending = res.trending
+        } catch {
+            errorMessage = (error as? LocalizedError)?.errorDescription ?? String(describing: error)
+            Log.api.error("Explore failed: \(self.errorMessage ?? "", privacy: .public)")
+        }
+    }
+
+    func browse() async {
+        isLoadingBrowse = true
+        errorMessage = nil
+        defer { isLoadingBrowse = false }
+        do {
+            let res = try await api.browseMarketplace(
+                query: browseQuery,
+                sort: browseSort,
+                language: browseLanguage
+            )
+            browseResults = res.items
+        } catch {
+            errorMessage = (error as? LocalizedError)?.errorDescription ?? String(describing: error)
+        }
+    }
+}