Initial commit: macOS terminal app with vertical tabs using libghostty

Features:
- Vertical tabs sidebar with SwiftUI
- Terminal emulation via GhosttyKit.xcframework (libghostty)
- Keyboard shortcuts: Cmd+T/N, Ctrl+Shift+` (new tab), Cmd+W (close),
  Cmd+Shift+[/], Ctrl+Tab (navigation), Cmd+1-9 (jump to tab)
- Reads Ghostty config from ~/Library/Application Support/com.mitchellh.ghostty/config
- Metal-based rendering

Sources/TabManager.swift

@@ -0,0 +1,73 @@
+import SwiftUI
+import Foundation
+
+class Tab: Identifiable, ObservableObject {
+    let id = UUID()
+    @Published var title: String
+    @Published var currentDirectory: String
+
+    init(title: String = "Terminal") {
+        self.title = title
+        self.currentDirectory = FileManager.default.homeDirectoryForCurrentUser.path
+    }
+}
+
+class TabManager: ObservableObject {
+    @Published var tabs: [Tab] = []
+    @Published var selectedTabId: UUID?
+
+    init() {
+        addTab()
+    }
+
+    func addTab() {
+        let newTab = Tab(title: "Terminal \(tabs.count + 1)")
+        tabs.append(newTab)
+        selectedTabId = newTab.id
+    }
+
+    func closeTab(_ tab: Tab) {
+        guard tabs.count > 1 else { return }
+
+        if let index = tabs.firstIndex(where: { $0.id == tab.id }) {
+            tabs.remove(at: index)
+
+            if selectedTabId == tab.id {
+                if index > 0 {
+                    selectedTabId = tabs[index - 1].id
+                } else {
+                    selectedTabId = tabs.first?.id
+                }
+            }
+        }
+    }
+
+    func closeCurrentTab() {
+        guard let selectedId = selectedTabId,
+              let tab = tabs.first(where: { $0.id == selectedId }) else { return }
+        closeTab(tab)
+    }
+
+    func selectTab(_ tab: Tab) {
+        selectedTabId = tab.id
+    }
+
+    func selectNextTab() {
+        guard let currentId = selectedTabId,
+              let currentIndex = tabs.firstIndex(where: { $0.id == currentId }) else { return }
+        let nextIndex = (currentIndex + 1) % tabs.count
+        selectedTabId = tabs[nextIndex].id
+    }
+
+    func selectPreviousTab() {
+        guard let currentId = selectedTabId,
+              let currentIndex = tabs.firstIndex(where: { $0.id == currentId }) else { return }
+        let prevIndex = (currentIndex - 1 + tabs.count) % tabs.count
+        selectedTabId = tabs[prevIndex].id
+    }
+
+    func selectTab(at index: Int) {
+        guard index >= 0 && index < tabs.count else { return }
+        selectedTabId = tabs[index].id
+    }
+}