refactor(deps): resolve openkal through the index rather than a branch

A released package that names a development branch is fragile: the branch is
not part of any release, and deleting it breaks a tarball that has already been
published. openkal 0.6.0 is in the index, so this reference names it.

Claude-Session: https://claude.ai/code/session_01Q4ucduLuSsETHYJ1RkGVVD

Author: Sunrisepeak

examples/hello/mcpp.toml

@@ -11,5 +11,5 @@ target  = "x86_64-windows-gnu"
 ldflags = ["-nostdlib", "-Wl,--subsystem,10", "-Wl,-e,efi_main"]
 
 [dependencies]
-openkal      = { git = "https://github.com/mcpplibs/openkal", branch = "feat/openkal-closure" }
+openkal = "0.6.0"
 openkal-uefi = { path = "../.." }

mcpp.toml

@@ -15,7 +15,7 @@
 [package]
 namespace   = "mcpplibs"
 name        = "openkal-uefi"
-version     = "0.1.1"
+version     = "0.1.2"
 description = "An implementation of openkal on UEFI Boot Services, for applications the firmware loads before an operating system exists"
 license     = "Apache-2.0"
 
@@ -32,7 +32,7 @@ authors     = ["mcpplibs"]
 repo        = "https://github.com/mcpplibs/openkal-uefi"
 
 [dependencies]
-openkal = { git = "https://github.com/mcpplibs/openkal", branch = "feat/openkal-closure" }
+openkal = "0.6.0"
 
 [build]
 flags = [