Fix tab titles not being preserved with window-save-state

Add serialization for tab titles in SurfaceView to persist user-set titles across app restarts. Bump TerminalRestorableState version to 4 to handle the new format.

macos/Sources/Features/Terminal/TerminalRestorable.swift

@@ -4,7 +4,7 @@ import Cocoa
 class TerminalRestorableState: Codable {
     static let selfKey = "state"
     static let versionKey = "version"
-    static let version: Int = 3
+    static let version: Int = 4
 
     let focusedSurface: String?
     let surfaceTree: SplitTree<Ghostty.SurfaceView>

macos/Sources/Ghostty/SurfaceView_AppKit.swift

@@ -1519,6 +1519,8 @@ extension Ghostty {
         enum CodingKeys: String, CodingKey {
             case pwd
             case uuid
+            case title
+            case isUserSetTitle
         }
 
         required convenience init(from decoder: Decoder) throws {
@@ -1533,14 +1535,27 @@ extension Ghostty {
             let uuid = UUID(uuidString: try container.decode(String.self, forKey: .uuid))
             var config = Ghostty.SurfaceConfiguration()
             config.workingDirectory = try container.decode(String?.self, forKey: .pwd)
+            let savedTitle = try container.decodeIfPresent(String.self, forKey: .title)
+            let isUserSetTitle = try container.decodeIfPresent(Bool.self, forKey: .isUserSetTitle) ?? false
 
             self.init(app, baseConfig: config, uuid: uuid)
+            
+            // Restore the saved title after initialization
+            if let title = savedTitle {
+                self.title = title
+                // If this was a user-set title, we need to prevent it from being overwritten
+                if isUserSetTitle {
+                    self.titleFromTerminal = title
+                }
+            }
         }
 
         func encode(to encoder: Encoder) throws {
             var container = encoder.container(keyedBy: CodingKeys.self)
             try container.encode(pwd, forKey: .pwd)
             try container.encode(uuid.uuidString, forKey: .uuid)
+            try container.encode(title, forKey: .title)
+            try container.encode(titleFromTerminal != nil, forKey: .isUserSetTitle)
         }
     }
 }