macos: quote input strings used for shell commands

When we're building an input string that's explicitly meant to be used
as a shell command, quote (escape) it using the same logic as Python's
shlex.quote function.

This specifically addresses issues we've seen when open(1)'ing Ghostty
with filename arguments that contain spaces.

macos/Sources/App/macOS/AppDelegate.swift

@@ -476,7 +476,7 @@ class AppDelegate: NSObject,
             // profile/rc files for the shell, which is super important on macOS
             // due to things like Homebrew. Instead, we set the command to
             // `<filename>; exit` which is what Terminal and iTerm2 do.
-            config.initialInput = "\(filename); exit\n"
+            config.initialInput = "\(filename.shellQuoted()); exit\n"
             
             // For commands executed directly, we want to ensure we wait after exit
             // because in most cases scripts don't block on exit and we don't want

macos/Sources/Features/App Intents/NewTerminalIntent.swift

@@ -68,7 +68,7 @@ struct NewTerminalIntent: AppIntent {
         // We don't run command as "command" and instead use "initialInput" so
         // that we can get all the login scripts to setup things like PATH.
         if let command {
-            config.initialInput = "\(command); exit\n"
+            config.initialInput = "\(command.shellQuoted()); exit\n"
         }
 
         // If we were given a working directory then open that directory

macos/Sources/Helpers/Extensions/String+Extension.swift

@@ -26,4 +26,12 @@ extension String {
         return self
     }
 #endif
+
+    private static let shellUnsafe = /[^\w@%+=:,.\/-]/
+
+    /// Returns a shell-escaped version of the string, like Python's shlex.quote.
+    func shellQuoted() -> String {
+        guard self.isEmpty || self.contains(Self.shellUnsafe) else { return self };
+        return "'" + self.replacingOccurrences(of: "'", with: #"'"'"'"#) + "'"
+    }
 }

macos/Tests/Helpers/Extensions/StringExtensionTests.swift

@@ -0,0 +1,19 @@
+import Testing
+@testable import Ghostty
+
+struct StringExtensionTests {
+    @Test(arguments: [
+        ("", "''"),
+        ("filename", "filename"),
+        ("abcABC123@%_-+=:,./", "abcABC123@%_-+=:,./"),
+        ("file name", "'file name'"),
+        ("file$name", "'file$name'"),
+        ("file!name", "'file!name'"),
+        ("file\\name", "'file\\name'"),
+        ("it's", "'it'\"'\"'s'"),
+        ("file$'name'", "'file$'\"'\"'name'\"'\"''"),
+    ])
+    func shellQuoted(input: String, expected: String) {
+        #expect(input.shellQuoted() == expected)
+    }
+}