Self-host Phase C: AOT link bootstrap targets and run native HelloWorld binary

[PurHur]

Goal

Phase C of #212: produce a native binary from bootstrap lint targets and execute examples/000-HelloWorld without Zend PHP.

Depends on

• Phase B ✅ (script/bootstrap-aot-lint.php green)
• Nullable params patch (merged with #TBD)
• Eventually Language: PHP namespaces (namespace, use, qualified names) #84 namespaces, Language: Class methods and property access in JIT #58/Language: Visibility, constructors, and destructors #145 class methods for lib/ entry points

Tasks

• bin/compile.php -o bootstrap-hello test/bootstrap-aot/echo_hello.php links on Linux/Docker
• Run ./bootstrap-hello and match VM output
• Document gaps in docs/bootstrap-selfhost.md
• CI: optional @group bootstrap job (skip when LLVM missing)

Non-goals

• Compiling lib/Compiler.php in this issue