Add unsaved-changes save prompt and crash-recovery draft

Replaces heuristic auto-save (goodbye-phrase detection, idle timeout,
min-message count, on-model-switch) with a standard macOS unsaved-changes
gate (Save/Don't Save/Cancel) on New Chat, Clear Chat, Load Conversation,
and Quit. The Save dialog gained a folder picker with inline "New Folder…"
creation.

Separately, the in-progress conversation is periodically mirrored to disk
(DraftRecoveryService, configurable interval in Settings, default 10s) and
offered back on next launch if oAI crashes or is force-quit, including the
model that was selected.

Two real bugs found via ObjectIdentifier/log-based diagnosis before this
worked correctly:
- oAIApp.init() wired AppDelegate.chatViewModel from its own @State read,
  which returned a throwaway ChatViewModel instance distinct from the one
  ContentView actually renders. Wiring moved to ContentView.onAppear.
- NSApplication.shared.delegate as? AppDelegate always failed silently:
  @NSApplicationDelegateAdaptor registers an internal SwiftUI.AppDelegate
  wrapper as the real NSApp.delegate (same name, different type in a
  different module), which forwards protocol methods but isn't castable
  to our type. AppDelegate now tracks itself via a static `shared`.

Also guards checkForCrashRecoveryDraft() against running under
XCTestConfigurationFilePath — oAITests is app-hosted, so xcodebuild test
launches this same app, and a leftover draft file on disk would otherwise
hang the entire test run on a blocking NSAlert with no one to click it.

oAITests/DraftRecoveryServiceTests.swift

@@ -0,0 +1,58 @@
+//
+//  DraftRecoveryServiceTests.swift
+//  oAITests
+//
+// SPDX-License-Identifier: PolyForm-Noncommercial-1.0.0
+// Copyright (C) 2026 Rune Olsen
+
+import Testing
+import Foundation
+@testable import oAI
+
+@Suite("DraftRecoveryService")
+struct DraftRecoveryServiceTests {
+
+    private func makeService() -> (DraftRecoveryService, URL) {
+        let url = FileManager.default.temporaryDirectory
+            .appendingPathComponent("oai-draft-test-\(UUID().uuidString).json")
+        return (DraftRecoveryService(fileURL: url), url)
+    }
+
+    @Test("load() returns nil when no draft file exists")
+    func loadReturnsNilForMissingFile() {
+        let (service, _) = makeService()
+        #expect(service.load() == nil)
+    }
+
+    @Test("save() then load() round-trips the draft")
+    func saveThenLoadRoundTrips() {
+        let (service, url) = makeService()
+        defer { try? FileManager.default.removeItem(at: url) }
+
+        let draft = DraftConversation(
+            messages: [Message(role: .user, content: "Hello"), Message(role: .assistant, content: "Hi there")],
+            conversationId: UUID(),
+            conversationName: "Test Conversation",
+            modelId: "anthropic/claude-sonnet-4-5",
+            savedAt: Date()
+        )
+        service.save(draft)
+
+        let loaded = service.load()
+        #expect(loaded?.messages.count == 2)
+        #expect(loaded?.messages.first?.content == "Hello")
+        #expect(loaded?.conversationId == draft.conversationId)
+        #expect(loaded?.conversationName == "Test Conversation")
+        #expect(loaded?.modelId == "anthropic/claude-sonnet-4-5")
+    }
+
+    @Test("clear() removes the draft file")
+    func clearRemovesFile() {
+        let (service, _) = makeService()
+        service.save(DraftConversation(messages: [Message(role: .user, content: "Hi")], conversationId: nil, conversationName: nil, modelId: nil, savedAt: Date()))
+        #expect(service.load() != nil)
+
+        service.clear()
+        #expect(service.load() == nil)
+    }
+}