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

Package.swift

@@ -0,0 +1,22 @@
+// swift-tools-version:5.9
+import PackageDescription
+
+let package = Package(
+    name: "GhosttyTabs",
+    platforms: [
+        .macOS(.v13)
+    ],
+    products: [
+        .executable(name: "GhosttyTabs", targets: ["GhosttyTabs"])
+    ],
+    dependencies: [
+        .package(url: "https://github.com/migueldeicaza/SwiftTerm.git", from: "1.2.0")
+    ],
+    targets: [
+        .executableTarget(
+            name: "GhosttyTabs",
+            dependencies: ["SwiftTerm"],
+            path: "Sources"
+        )
+    ]
+)