Add 6 new practice features, offline dictionary, and feature reference

New features:
- Offline Dictionary: reverse index of 175K verb forms + 200 common
  words, cached to disk, powers instant word lookups in Stories
- Vocab SRS Review: spaced repetition for course vocabulary cards
  with due count badge and Again/Hard/Good/Easy rating
- Cloze Practice: fill-in-the-blank using SentenceQuizEngine with
  distractor generation from vocabulary pool
- Grammar Exercises: interactive quizzes for 5 grammar topics
  (ser/estar, por/para, preterite/imperfect, subjunctive, personal a)
  with "Practice This" button on grammar note detail
- Listening Practice: listen-and-type + pronunciation check modes
  using Speech framework with word-by-word match scoring
- Conversational Practice: AI chat partner via Foundation Models
  with 10 scenario types, saved to cloud container

Other changes:
- Add Conversation model to SharedModels and cloud container
- Add Info.plist keys for speech recognition and microphone
- Skip speech auth on simulator to prevent crash
- Fix preparing data screen to only show during seed/migration
- Extract courseDataVersion to static property on DataLoader
- Add "How Features Work" reference page in Settings

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Conjuga/Conjuga/Views/Practice/Chat/ChatView.swift

@@ -0,0 +1,150 @@
+import SwiftUI
+import SharedModels
+import SwiftData
+
+struct ChatView: View {
+    let conversation: Conversation
+
+    @Environment(\.cloudModelContextProvider) private var cloudModelContextProvider
+    @State private var service = ConversationService()
+    @State private var messages: [ChatMessage] = []
+    @State private var inputText = ""
+    @State private var errorMessage: String?
+    @State private var hasStarted = false
+
+    private var cloudContext: ModelContext { cloudModelContextProvider() }
+
+    var body: some View {
+        VStack(spacing: 0) {
+            // Messages
+            ScrollViewReader { proxy in
+                ScrollView {
+                    LazyVStack(spacing: 12) {
+                        ForEach(messages) { message in
+                            ChatBubble(message: message)
+                                .id(message.id)
+                        }
+
+                        if service.isResponding {
+                            HStack {
+                                ProgressView()
+                                    .padding(.horizontal, 16)
+                                    .padding(.vertical, 10)
+                                    .background(.fill.quaternary, in: RoundedRectangle(cornerRadius: 16))
+                                Spacer()
+                            }
+                            .padding(.horizontal)
+                        }
+                    }
+                    .padding(.vertical)
+                }
+                .onChange(of: messages.count) {
+                    if let last = messages.last {
+                        withAnimation { proxy.scrollTo(last.id, anchor: .bottom) }
+                    }
+                }
+            }
+
+            Divider()
+
+            // Input
+            HStack(spacing: 8) {
+                TextField("Type in Spanish...", text: $inputText)
+                    .textFieldStyle(.roundedBorder)
+                    .autocorrectionDisabled()
+                    .textInputAutocapitalization(.sentences)
+                    .onSubmit { sendMessage() }
+
+                Button {
+                    sendMessage()
+                } label: {
+                    Image(systemName: "arrow.up.circle.fill")
+                        .font(.title2)
+                }
+                .disabled(inputText.trimmingCharacters(in: .whitespaces).isEmpty || service.isResponding)
+                .tint(.green)
+            }
+            .padding()
+        }
+        .navigationTitle(conversation.scenario)
+        .navigationBarTitleDisplayMode(.inline)
+        .alert("Error", isPresented: .init(
+            get: { errorMessage != nil },
+            set: { if !$0 { errorMessage = nil } }
+        )) {
+            Button("OK") { errorMessage = nil }
+        } message: {
+            Text(errorMessage ?? "")
+        }
+        .onAppear {
+            messages = conversation.decodedMessages
+            if !hasStarted && messages.isEmpty {
+                startConversation()
+            }
+            hasStarted = true
+        }
+    }
+
+    private func startConversation() {
+        let opening = service.startConversation(scenario: conversation.scenario, level: conversation.level)
+        let msg = ChatMessage(role: "assistant", content: opening)
+        conversation.appendMessage(msg)
+        messages = conversation.decodedMessages
+        try? cloudContext.save()
+    }
+
+    private func sendMessage() {
+        let text = inputText.trimmingCharacters(in: .whitespaces)
+        guard !text.isEmpty else { return }
+
+        let userMsg = ChatMessage(role: "user", content: text)
+        conversation.appendMessage(userMsg)
+        messages = conversation.decodedMessages
+        inputText = ""
+        try? cloudContext.save()
+
+        Task {
+            do {
+                let response = try await service.respond(to: text)
+                let assistantMsg = ChatMessage(role: "assistant", content: response)
+                conversation.appendMessage(assistantMsg)
+                messages = conversation.decodedMessages
+                try? cloudContext.save()
+            } catch {
+                errorMessage = "Failed to get response: \(error.localizedDescription)"
+            }
+        }
+    }
+}
+
+// MARK: - Chat Bubble
+
+private struct ChatBubble: View {
+    let message: ChatMessage
+
+    private var isUser: Bool { message.role == "user" }
+
+    var body: some View {
+        HStack {
+            if isUser { Spacer(minLength: 60) }
+
+            VStack(alignment: isUser ? .trailing : .leading, spacing: 4) {
+                Text(message.content)
+                    .font(.body)
+                    .padding(.horizontal, 14)
+                    .padding(.vertical, 10)
+                    .background(isUser ? AnyShapeStyle(.green.opacity(0.2)) : AnyShapeStyle(.fill.quaternary), in: RoundedRectangle(cornerRadius: 16))
+
+                if let correction = message.correction, !correction.isEmpty {
+                    Text(correction)
+                        .font(.caption)
+                        .foregroundStyle(.orange)
+                        .padding(.horizontal, 4)
+                }
+            }
+
+            if !isUser { Spacer(minLength: 60) }
+        }
+        .padding(.horizontal)
+    }
+}