fix: install each library target individually instead of phony target

The phony `xpkg` target produces no installable artifacts. Install
each of the 5 real library targets individually to properly export
module files and static libraries while avoiding examples/tests.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Sunrisepeak

packages/m/mcpplibs-xpkg/xmake.lua

@@ -15,5 +15,11 @@ package("mcpplibs-xpkg")
 
     on_install(function (package)
         local configs = {}
-        import("package.tools.xmake").install(package, configs, {target = "xpkg"})
+        local install = import("package.tools.xmake").install
+        -- Install each library target individually to avoid building examples/tests
+        install(package, configs, {target = "mcpplibs-xpkg"})
+        install(package, configs, {target = "mcpplibs-xpkg-loader"})
+        install(package, configs, {target = "mcpplibs-xpkg-index"})
+        install(package, configs, {target = "mcpplibs-xpkg-lua-stdlib"})
+        install(package, configs, {target = "mcpplibs-xpkg-executor"})
     end)