restore: ghostty.h bridge header — CI contract, not dead code

scripts/ensure-ghosttykit.sh validates that the root ghostty.h re-exports
ghostty/include/ghostty.h and fails the GhosttyKit source-build fallback
without it (compat-tests and ui-regressions both went red when the prebuilt
xcframework download 404'd and the fallback ran). No Swift/C file includes
it, but the build system treats it as a contract. Reclassified as Deferred:
removing it means also removing the guard, which is a maintainer call.

Author: arzafran

GhosttyTabs.xcodeproj/project.pbxproj

@@ -255,6 +255,7 @@
 		A5001544 /* TerminalImageTransfer.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TerminalImageTransfer.swift; sourceTree = "<group>"; };
 		A5001545 /* TerminalSSHSessionDetector.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TerminalSSHSessionDetector.swift; sourceTree = "<group>"; };
 			A5001016 /* GhosttyKit.xcframework */ = {isa = PBXFileReference; lastKnownFileType = wrapper.xcframework; path = GhosttyKit.xcframework; sourceTree = "<group>"; };
+		A5001017 /* ghostty.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = ghostty.h; sourceTree = "<group>"; };
 		A5001018 /* programa-Bridging-Header.h */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.c.h; path = "programa-Bridging-Header.h"; sourceTree = "<group>"; };
 		A5001019 /* TerminalController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = TerminalController.swift; sourceTree = "<group>"; };
 		A5FF0004 /* TerminalController+BrowserAutomation.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "TerminalController+BrowserAutomation.swift"; sourceTree = "<group>"; };
@@ -489,6 +490,7 @@
 				A5001101 /* Assets.xcassets */,
 				A5001016 /* GhosttyKit.xcframework */,
 				A5001018 /* programa-Bridging-Header.h */,
+				A5001017 /* ghostty.h */,
 				3196C9C2D01F054C1D3385DD /* programaUITests */,
 				F1000003A1B2C3D4E5F60718 /* programaTests */,
 				A5001042 /* Products */,

ghostty.h

@@ -0,0 +1,8 @@
+#ifndef CMUX_GHOSTTY_BRIDGE_HEADER_H
+#define CMUX_GHOSTTY_BRIDGE_HEADER_H
+
+// Keep the Swift bridge on Ghostty's canonical C API header so Xcode and the
+// bundled GhosttyKit stay ABI-aligned across submodule upgrades.
+#include "ghostty/include/ghostty.h"
+
+#endif